A Tale of Two Questions

This past week I had a quiz for each of my Geometry sections. The two sections are out of synch a bit due to our rotating schedule. They typically assess on different days with different versions of whatever quiz or test I recently wrote. This week’s quiz had two different forms of the final question. I present them below:

In the diagram below you see a triangle ABC and you see what are called the exterior angles of the triangle marked. What is the sum of the measures these exterior angles? Be careful to carefully show your reasoning. Mark any angles clearly that you want to refer to in your explanation.  

The problem above was presented to my class on Thursday.

In the diagram below you see a triangle ABC and you see what are called the exterior angles of the triangle marked. The sum of these exterior angles is 3600. Write a proof explaining to me why this is true. Mark any angles on the diagram that you refer to in your proof.

The problem above was presented to my class on Friday.

Both classes had the same first problem on their quiz. They were asked to prove that the interior angles of a triangle sum to 180 degrees. This proof was explicitly presented in class and in their text. My thought was that this challenging fifth problem should be a (somewhat) natural consequence of the first problem on the quiz.

The students who took the quiz on Thursday struggled on the first problem and it bled over to the last. They generally performed better on the last problem than on the first. In part, this is due to my decisions about partial credit. I was definitely more generous with partial credit on the problem at the end of the quiz since they had not seen any explicit proof of this fact. My colleague who also teaches Geometry felt that I might be reaching a bit with this last question. My Friday class performed better on the first proof than the Thursday crew and they did a MUCH better job on the last problem. I am trying to sort this out and there are too many variables at play. First, the class who took the quiz on Friday has performed at a slightly, but consistently, higher level overall during the first trimester of our year. Second,there is always the possibility that information about the quiz was discussed in a way that gave the Friday class some advantage. Finally, the problem presented to them gave an answer and asked for justification while the problem as presented to the Thursday class did not provide the conclusion. I was more strict with partial credit with the Friday quiz class since the conclusion was given to them and the whole burden of the problem was the explanation.

The main reason I am writing about this is that I am trying to make myself think clearly about what my goals are in a  problem like this one and to convince myself that I was trying to get at the same thing with both classes. Did I drastically change the nature of what was being assessed by presenting the conclusion already? I have thought out loud on this blogspace about a similar question here – https://mrdardy.mtbos.org/2017/09/22/a-quick-question-about-test-questions/

Did revealing the answer to the question fundamentally change the level of challenge inherent in the question? Is it THAT much easier to reason through the proof when you know what you are supposed to conclude?

Our Geometry course is the last course in our curriculum where there is no Honors option. Everyone who takes geometry takes the same course at our school. This means that there is a wider variety of interest and talent in this room than in my other classes. I think that there is a tendency in a non-honors math class to think that the students cannot tackle challenging or novel questions. I have heard several colleagues over the years say something along the lines of ‘I can’t ask that question if I haven’t shown them how to do it.’ These are terrific teachers saying this and they are coming from a good place, they want their students to succeed and they do not want them discouraged or dismayed by assessments. I think I am coming from a good place as well, it’s just a different place. I’d also say that in the case of the question above, especially in its first form, I do believe that I have shown my students how to tackle such a question. They know that the interior angles sum to 180 degrees. They see three supplementary pairs of angles so that sum is 540 degrees. The difference is the exterior angles. Half of the students in the Thursday group earned four or five points out of five on the problem. Those who earned four generally had sound logic with real flaws in the vocabulary explaining their answers. Maybe my docking them a point is an entirely different question about how I assess.

Another reason I am writing this is that I want to have a conversation with my department about questions like this one, questions that are not a simple transformation of what has already been practiced. I have students who imply that I am the first teacher they have who asks them questions that feel like they might be ‘from left field.’ I know that students (all people, really) will exaggerate their concerns in the face of feeling stressed. I think most of my students do a nice job of stepping up to challenges like this one, especially when points are riding on it on an assessment. But I also know that there is an instinct at times to simply dodge these situations. The same group of kids who took the quiz on Thursday were presented with a problem from Steve Wyborney’s website on Friday in class. I showed them the video of the duplicator lab problem.  When the video ended I asked them to begin talking about the problem with their neighbors – in this class everyone sits in groups of three that get randomly reassigned every fifth day. I was met with mostly silence. To be fair, this was about 8:10 in the morning. However, when I showed them the comments section with teachers talking about their fourth and fifth graders solving the problem, they suddenly started talking. So, I don’t know if they were shamed into action or they simply needed to suspect that they were more than capable of solving the problem before they moved. I have to feel that the struggle with the problem on Thursday and their reluctance to engage with a novel problem on Friday morning are related. I also fear that I have not done enough yet to create a culture where they jump into these problems. I am interested in how the conversation goes with my department on Wednesday morning and I would love to hear from any readers as well.

 

Persistence and Creativity

I spent six hours yesterday watching students take final exams. Three two-hour shifts. Sigh…

My last group taking an exam was my AP Calculus BC team. They had 24 multiple-choice questions and four free response questions, so they had to be efficient in their problem-solving. One of my students asked me about a multiple choice question that troubled him. It was an infinite geometric series question. This student joined our school, and our country, last year as a freshman. He place tested so highly that he started in AP Calculus AB. However, it has become apparent that there are a few facts/skills that he does not have at his command. This is rarely a problem since he is so creative. On this question, he did not have the formula in his brain for calculating the sum of an infinite geometric series. He could have listed out a handful of terms to look for convergence. He could have shrugged his shoulders and guessed since it was one of twenty-four questions. Instead, he wrote a short program on his TI-84 that gave him increasingly good approximations until he saw one of the answer choices emerge. He did this in the middle of a two-hour exam! He asked me afterwards and just laughed when I showed him how easy this problem could have been. I am convinced that he will remember this formula forever now, but I am also convinced that I will remember this story forever now. His ability to problem-solve in this situation is SO much more powerful than having a formula at his command. It is interesting that this happened on the same day that I sent our a question on twitter about the use of formula sheets on assessments. I am disinclined to use formula sheets, but I could be convinced otherwise. Here is a story that would have never happened if a formula sheet was present.

I am going to cross post this over at the One Good Thing blog space.

 

Another Fun Problem Debate

A super quick post this morning. On my last problem set for AP Calculus BC I included the problem below:

A 10 m rope is fastened to one of the outside corners of a house, which has the form of a rectangle, 6 m long and 4 m wide. A dog is fastened to the rope. What is the perimeter of the region that the dog can access?

I have asked a form of this question a couple of times over the years. One year I did not mention that the rope was on the exterior of the house and I had a student assume that the dog was tied to a leash inside the house. I fixed that mistake.

A GeoGebra sketch below shows the image I have in my head for this problem.  

My answer to this question, and the answer that 11 of my 14 students had, was that the perimeter is 20π. Two students argued that the answer should be 20π + 20. Their argument is that the borders of the house, the sides of the rectangle in the drawing, are also part of the perimeter. I loved the debate that ensued and most students migrated to this point of view. I reflexively thought of perimeter as exterior, while these two students argued that perimeter is boundary. I think I agree with them and I LOVE the fact that they cared enough to debate this on a problem that counted for one point out of about 400 something for the term. I also LOVE that students who got their answer marked correct started arguing against the answer that they arrived at.

AP Calculus BC – A Lovely Debate

It has been WAY too long since I posted. Energy has been scattered in a number of directions lately…

 

Yesterday in AP Calculus BC their sixth problem set of the year was due. I heard quite a bit of debate among my young scholars about one question in particular. Here it is:

I wish I remembered where I found this problem. I know I have used it in the past but I do not remember much debate about it. A little background about how I approach these problem sets before I relate the conversation we had. We are on a seven day class rotation in our new schedule. This rotation sometimes even includes two weekends. I assign a problem set the first day we meet on each rotation and it is due the first day of the next rotation. My students have time to wrestle with these problems, to ask each other questions, ask me questions, look up ideas/clues/data/etc. These are sets of ten problems and they only count ten points. All of the problem sets together count about as much as one test in a term. By the time the term is up, each problem set will end up weighing about 2 – 3% of a term grade. I grade them pretty easily, looking mostly for thoughtful process and I am willing to deal with half points which feels a bit silly but it honors thoughtful work rather than whacking them for some little mistake. Anyway, the point here is that these should be low stress and they should encourage collaborative thought and work. I have been clear that I encourage them to think together. Anyway, when they came into class yesterday there were a flood of questions for each other about fine points of interpretation for this problem and students were asking me about two distinct interpretations of part b of the problem. I loved the debate, I just wish it had been happening more than 2 minutes before the work was due. The primary debate was whether to answer part b by interpreting the year as the interval from 0 to 12 or whether to interpret it as 1 to 13. Our friend GeoGebra helped us a bit. Three screen shots below: 

Now, the curve with the integral from 0 to 12 highlighted: 

Finally, the curve with the integral from 1 to 13 highlighted: 

Nice, right? The area is the same according to GeoGebra. What followed was such a highlight of my day. Intense debate about why these seem to be the same. One student notes that the obnoxious coefficient for x in the function yields a period of essentially 12. Not a surprise, right? Nice observation. A nice debate about the limits. Is 1 the end of January or the beginning? I feel it needs to be the end of the month the way the problem is written, so I came down on the side of 1 to 12 as the proper integral. An observation about the symmetry of right Riemann sums where some months have overlaps and others have underestimates. Another nice observation.  One student questions this model because he notes, as a northern city, Seattle should have more rain in the warmer weather months rather than have this mediterranean rainfall pattern. Wow. I pointed out that I know people who lived in Seattle and have visited there and that this is indicative of what I know about the area. I do not think that this would have ever occurred to me! A debate about whether we simply want to add f(1) + f(2) + f(3) + … + f(12) rather than integrate. One student mentions that he looked up the yearly rainfall in the Seattle area and the answer he found was pretty close to our integral. Good golly, that made me happy. A student questioned whether I wanted two answers to part a. I admitted that the word extreme, in this context, only made me think of a Maximum. I admitted that I should have been more careful than to make that assumption and I should include the minimum in the answer to part a as well.

We have a test today, so I pivoted the class conversation toward some practice problems but I felt that there was probably still more to discuss about this problem. Days like yesterday remind me of how spoiled I am that I get to do math with a group of scholars that are willing to engage in energetic debate about math. They are rarely interested in just knowing the answer, they seem to genuinely enjoy to process that gets them there. I am not going to pretend that all 15 students were actively engaged joining in with their ideas. I will say that there were all at least attentive and willing to let the conversation flow without pointing out, anxiously, that we need to talk about the upcoming test.

We decided a number of years ago to teach BC as a second year Calculus course at our school. We know that many of our students can accelerate through the BC curriculum in one fast year or by buying some Precalculus Honors time, but conversations like this one would be hard (not impossible) to find time for. Every year I hear a scholar say something along the lines of ‘I knew how to do this before but now I think I know why it works.’ Statements like that one, and conversations like yesterday’s make me feel good about this curriculum decision we made.

Checking in on a new Policy

I recently blogged about a commitment made by our math department. As a reminder to you, dear reader, here is the statement from one of my course syllabi:

Beginning in the 2017 – 2018 academic year, our math department is adopting a policy of expecting test corrections on all in-class tests. The policy is described below.

  • When grading tests initially each question will get one of three point assignments
    • Full credit for reasonable support work and correct answer.
    • Half-credit for minor mistakes as long as some reasoning is shown.
    • Zero credit (in very rare cases) when there is no reasonable support shown or if the question is simply left blank.
  • When grading tests, I will not put comments, I will simply mark one of these three ways.
  • You will be allowed to turn in corrections. Corrections will be on separate paper and will have written explanations of errors made in addition to the correct work and answer. This work is to be in the student’s words but can be the result of consultation/help. These corrections will always be due at the beginning of the second class meeting day after the assessment is returned. You will return your original test along with your correction notes. I will remind you of this every time I return a graded test to you.
  • It is not required that you turn in test corrections.
  • The student can earn up to half of the points they missed on each individual problem.
  • This policy does not apply to quizzes, only to in-class tests.

There are  a couple of items in the learning curve to report on here. I will lead with the positives –

  • We have an after school conference time that many students take advantage of for extra help. My room has been more crowded this year than it has been for years. I take this as a plus sign that students are committed to seeking help and investing in their math studies. Many of them are there talking with me and with their classmates about test corrections.
  • I have had a number of students turn in their corrections the same day that they received their tests. It is a rare thing for students to turn in work days early, it is happening regularly right now.
  • I walked out of my classroom today with a new student who was talking excitedly about how she is really thinking carefully about her work and she is sure that she’ll remember material better because of this.
  • It is faster to return tests since I am simply marking them 100%, 50%, or 0% for each problem.

Now a few negatives, followed by some philosophical pondering about this whole endeavor.

  • I anticipated that there would be very few zero scores on problems. There have been more than I thought but I hope that is a factor of students learning to show some work. This may be a positive as a zero stings a bit and they may be more inclined to be careful in their explications.
  • Some students feel stung by relatively minor mistakes that initially result in a 50% on an individual problem. These minor mistakes turn into 75%. I am trying to point out that relatively major mistakes can also end up at the 75% level but some students feel a bit cheated.
  • Early in the year averages fluctuate quite a bit anyway, but the fluctuations are exaggerated in this system. I see already that overall averages are a bit higher than normal and there is much less variance in scores. However, some students are scared since they have a hard time seeing the long game as clearly.
  • Explaining this to folks outside the department has been a bit of a challenge.

 

When I was working on my doctorate I had a professor (my thesis advisor) who had a policy that every paper will be rewritten, not just every paper can be rewritten. The way he did this was to return our first drafts with no comments, just hash marks in the margin at certain points of the paper. These hash marks might be there to point out a flaw in our argument or our paper’s structure. They might also indicate a highlight. They might indicate a misspelling or a simple grammar problem. He was willing to discuss these hash marks in his office hours as long as it was clear that we had sound questions about them, in other words we had to prove to him that we had reflected on our writing. I have never thought so much about my own writing as I did in that class. I do not expect my 14 year olds to do this kind of self analysis, but I know that they ARE capable of careful reflection if they are given the time, space, and motivation to do so. What I am seeing when they come to me is that they have looked over their test, they have referenced notes and their HW. They have done careful thinking and they can usually explain their mistake on their own. This is not universal, but it is happening more often than not. Many students who come to my room to work on corrections have almost no question for me. They are berating themselves for ‘stupid mistakes’, they are laughing at silly things they wrote, they are even saying ‘I have no idea what this work means’ I am pretty convinced that this can be a huge growth opportunity for my students. They are being responsible for their own error analysis here and they are writing thoughtful reflections in the form of ‘On problem 4 I made this mistake, I should have done this instead’

We have midterm grade comments looming and as department chair I know I will have some questions coming my way about our reasoning and the long-term impact on grades. I will try to steer the conversations to long-term impact on learning and self-sufficiency. So far the policy has exceeded my hopes in my classes. I will be checking in with my department to get other points of view soon and I plan on sharing some of those conversations as well.

 

Should My Preferences be my Students’ Preferences?

At the beginning of every year I am reminded that there are little quirks I have about how I would like to see answers presented and I have this silly assumption that my brand new students should just know what I want. I wish that I remembered this in August and prepped myself and my students with some conversations. I am writing this brief post this morning while one of my classes is taking a test. I would love some feedback here in the comments or over on twitter where I am @mrdardy

I just graded my first problem set from my AP Calculus BC wizards. One of the questions asked for the point on the curve y = x^(1/2) that was closest to the point (4,0). Everyone correctly identified x = 3.5 as the critical x value and about half of them identified (3.5)^(1/2) or sqrt(3.5) [my LaTex skills are weak and I am in a bit of a hurry…] as their y-coordinate. However, about half of them gave me a three decimal approximation. For reasons I cannot completely justify it makes me nutty to see a less exact answer written as an extra step in their work. I know that their science teacher is not interested in radicals in their answers. I know that carpenters do not have radicals on their measuring tapes. I also know that all of my Calc BC kiddos had the exact value for y written at one point in their solutions and many chose to do a little extra writing to make their answer less exact. Am I being a crank if I make this a point of conversation? Along the same lines, I urge them not to rationalize but many cannot help themselves. I urge them to leave a line equation in point-slope form when that is one of the steps in their problem-solving process. I ask them to write x < 3 rather that 3 > x, especially in a piecewise function where I want to read through their domain in order.

These are tiny, tiny problems to focus on. I recognize this. But I also know that I will spend many months with this group of students and I want them to understand my thoughts since I am asking them to routinely explain theirs on paper to me. I would love to hear points of view about how important any of these habits are for kids of this caliber. I am completely open to recognizing that these are just weird little quirks of mine, but I also hope that there is some mathematical logic underlying all of this. Please drop a line to let me know what you think and how you have responded to students in your efforts to help them develop a clear and consistent strategy for communicating their mathematical ideas.

So, What Kinds of Change?

In my last post I wrote about our department’s terrific two day workshop with Henri Picciotto. One of the major decisions we made based on the time we spent together is that we have decided, as a whole department team, is that we will allow test corrections on all tests in our department. Before I dive into the format of the decision we made, I want to include a couple of important links here with other points of view about assessment policies. The first comes from a new twitter contact Steve Gnagni (@Steve_Gnagni) who shared this interesting document written by Rick Wormeli (@rickwormeli AND @rickwormeli2 for reasons I am not sure I understand!) called Redos and Retakes Done Right and the second is a link Henri shared gathering together some of his ideas about assessments.

So, a little history here about where I am as a teacher and where I, and my team, hope to move. In the past three years I have had a policy in some of my classes. In any class where I have been the only teacher I have allowed test retakes. If you are unhappy with your test score, make an appointment to sit with me and look at what went wrong on your test and sometime within the week that your test was returned, you can take a new version of this test. Originally, I averaged the two test scores but this year I weighted the retest so that the score that stayed int he grade book was two parts retest and one part original test.  I also told students that anyone who scored below a 70% on the assessment were expected to take the retest. I did not do this in classes where I was part of a team teaching the course since not everyone agreed with this policy. The advantages of this policy were that students who were struggling to master material and perform on tests felt that they still had a lifeline. Those students were more likely to follow up with me and try to figure out what went wrong with their original attempt. Students were willing to take the extra time and energy to try and improve and I had reason to believe that material was sticking a bit better for many of my students. The primary disadvantages? This created quite a bit of extra work for me writing and grading reassessments. Some students seemed stuck on a perpetual hamster wheel of assessments and a handful of students were very honest about the fact that they sometimes pushed my assessments down their list of priorities since they knew this lifeline existed. This was a small group of students but enough that I was questioning the wisdom of this policy.

When Henri was with us he spoke passionately about the advantages of students correcting their own work. He talked about a cycle of student reflection and about the burden of careful written feedback on assessments. A sad fact is that most students (we probably know this about ourselves from when we were students) simply look to the grade. While many of us take careful time to highlight problems and write notes or to write congratulatory notes for work done especially well, much of this probably falls into the cracks. I know that I have read research – and I wish I could find it quickly – about the tension between writing comments on papers and writing grades on papers. These two forms of information for our students do not work in support of each other. So, after some conversation with Henri and then a long, productive final faculty meeting in the week after Henri left, we came up with a policy that we feel pretty good about. On unit tests when we grade them the first time we will assign one of three options to each problem. If the problem is done well, clear work and a correct answer (or a minute problem like some minor arithmetic error) that problem will receive full credit. If a problem shows no sign of clear explanation and no clear sign of understanding that problem will receive a zero. The vast world of problems in between these two poles will receive half credit. We will not highlight or circle errors in solutions. We will not write notes about the problem-solving process. We will simply return the paper with an initial grade. We will be able to do so quickly under these circumstances. The students will then have time to take this assessment and rework any problem that received less than full credit. They can earn back half the points that they missed by submitting corrections. The resubmission will have the original paper and two requirements for earning back points. They will need to submit correct solutions AND they will need to submit a written reflection/explanation of what went wrong and how it was corrected. Students can meet with each other, they can ask their teacher for guidance in our extra help sessions, they can look at their notes and their text, in general they can seek any kind of help. Some will inevitably just take the word of someone or something (like Wolfram Alpha) but ALL will be encouraged to take some time to reflect. ALL will be allowed to earn back some part of the points that they missed. ALL will know that test day is not such a high stakes day where it is do or die. There will be some bumps along the way as we train ourselves and our students to take this process seriously. We will have to be very conscious early in the year about establishing standards for what these written explanations need to look like. The student who earned a 60% the first time has a meaningful lifeline. The student who earned an 85% the first time still has motivation to rework and rethink the material. We will need to think about timelines, especially near the end of a grading term, but these are good problems to have and good conversations to make public. Teachers will be talking to each other about this process as we unpack it. Students will be encouraged to talk to each other about math and to seek guidance from each other. This will feel like a serious sea change for our department, I am totally excited about it.

Or, I should say I was totally excited about it. I know that there are different ways to view this process and the meaning of it. I know that we decided that events that we call tests are subject to this correction policy. We decided (for a number of reasons, some more ideologically defensible than others) that short quizzes were not subject to this policy. I know that I will be balancing this with graded take-home problem sets and on these problem sets I always encourage collaboration. So, when Steve Gnagni shared the article above, I found myself doubting some of the decisions we made. I found old reactions about grades being really seriously challenged and I began to doubt whether our decision on process is ideologically pure enough. I also know that this is progress. I will be sharing Rick Wormeli’s article with my team in the fall and we will be checking in with each other on how we feel about the impact of this new process.

I want to thank Henri again and to thank my new twitter pal Steve Gnagni for sharing their ideas. As long as we are all willing to keep questioning ourselves we can continue to help our students grow.

My Students are Making Some Smart Guesses

On Friday in Geometry we were continuing our conversation about triangle centers and I asked my students to find the point where medians coincide in a scalene triangle. There is a good amount of algebraic detail in these problems but my students were doing a nice job pushing through this problem. After finding the centroid, I asked them to form a new triangle from the three midpoints we needed when considering medians. We found the perimeter of the original triangle and I asked also for the perimeter of the triangle formed by the midpoints. One of my students theorized that the new triangle would have one-fourth the perimeter of the original triangle. I asked the other students to quiet for a moment to hear this guess. Before asking GeoGebra to check his answer he quickly corrected himself and said he was thinking about area, not perimeter. A beautiful realization on his part that this triangle formed by midpoints would divide the original triangle into four equal areas. Just as we were congratulating him for this guess another students asked about equilateral triangles. He wondered aloud whether the midpoint triangle in an equilateral triangle would form four equilateral triangles. I realized he was asking whether the triangles formed in the scalene we were looking at were also congruent, not just equal in area. A quick question from me confirmed my guess so we drew our attention again to the GeoGebra sketch we had up. He was able to identify where the congruent angles were that allowed us to prove congruence for the triangles.

This conversation was a wonderful way to end our day on Friday. I am delighted that my students are comfortable enough to make these guesses out loud and even more delighted that they are making such good guesses right now. I pointed out how helpful it is to play with GeoGebra to check these guesses and I hope (I hope hope hope!) that some of my students are making a habit of this.

A Delightful Conversation

Last week in my Geometry class we had a fantastic conversation about a homework problem. Here is the problem in question –

screen-shot-2016-12-06-at-3-56-52-pm

 

I wish that I could take credit for having written this, but I am certain that I ‘borrowed’ it from somewhere. Likely from the fantastic resources shared with me by Carmel Schettino (@SchettinoPBL)

So, this is the kind of problem that I expect only a minority of my students to navigate successfully on their own, but I am convinced that almost all of them will benefit from thinking about a problem like this one, from a little active struggle along the way. I KNEW that this would be asked in class if anyone took the time to do the HW I assigned, so I was pleased that it came up. I started by telling my students that I LOVE this problem and asked them if they could guess why. One student said ‘Because it’s so hard’. I laughed that off and said, yes it is hard but I love it because it ties together a bunch of important ideas. Off we went on solving this. I started by asking a couple of questions that probably seemed a bit irrelevant at first. I asked why they knew that the y-intercept was (0, 3) and that the x-intercept was (4, 0). Before they could answer I made sure to mention that they knew this without looking at the graph. We eventually arrived at the realization that we know whether a point is on the line or not by looking at the equation itself. If a point makes the equation true, then that point is on the line. If not, then not. This is the kind of thing that I think my students know but being reminded regularly sure does help reinforce it. I hope! So, I thought I had set the hook here for the rest of the problem. We talked about what we know about squares and we talked about how to identify points on the square without knowing their real coordinates. We got a little lazy, and I was okay with that,by calling the bottom right corner (x, 0) and the top left corner (0, y). This gave us no choice but to call the top right corner of the box (x, y). At this point I paused and asked them to remind me what needs to be true about points on a line. Then I asked them to remind me of what we know about a square, therefore what we know about x and y for that mystery point (x, y). It wasn’t easy to get everyone to agree with our conclusions, but I think we got there. We agreed that the x and the y had to equal each other. We agreed that the y coordinate had a definition based on x. We agreed that this was an equation we could solve even though it was not a bunch of fun to solve it. After all of this work it felt like the problem should be done, students were pretty sad to realize it wasn’t. We still had a conclusion to make about the triangles created. One of my students was pretty insistent that they needed to be congruent because their angles had to match up. This was not the time to launch into a conversation about similarity and I decided it was not the time to talk about the restrictions of AAA conclusions between triangles. We have talked about equilateral triangles of different sizes and we are (mostly) okay with that, but I felt that that conversation would be a diversion here. Instead, we kept at the calculating and we looked at side lengths. Once we agreed that they were not congruent, I pointed to the slope of the line and talked about the fact that his instinct was foiled by the fact that x and y lengths were not changing at the same rate. The whole conversation took quite some time, might have been 15 minutes by the time the whole thing was done, but I felt that we had done some important heavy lifting.

If you recognize the above problem as your own, feel free to claim it and let me know. Know in advance that I am very grateful for such a rich problem to tie together ideas of distances, slopes, line equations, properties of squares, and triangle congruencies all into one tidy package!

 

Hands-On Geometry

I’ve been at this high school math gig for a good long while now but I periodically have to remind myself of a couple of important facts. The most important one is that not everybody’s mind works like mine. Just because I like a certain way of thinking, or dislike a certain way of learning, I should not assume all my students will agree. In fact, I can be pretty certain that all of my students will not agree, there’s too many individuals for that to work.

When I studied Geometry I did not like physical drawings and constructions. In part because I am a bit inept when it comes to controlling something like a compass, but also because getting my hands engaged does not seem to fire too many of my neurons. So, when I wrote my Geometry book a couple of years ago I did not include much in the way of hands-on manipulations. The past couple of years of working through the text with our students has pointed out the weakness of this approach. So, I put my head together with one of my talented colleagues to try and make an activity that would trigger some neurons for those students who come to life when they get their hands busy. I had been using a pretty cool activity I ran across from Jennifer Silverman but I made pretty flimsy paper copies to work with on a pipe building activity where kids had to manipulate bent angle joints with different pipe lengths. It’s a great activity but using simple paper copies dragged the activity down. We invested in some packs of AngLegs this year and my colleague wrote a pretty cool activity modeled off of our pipe building activity. You can find his document here.

I was impressed as each of the seat groups in my class played with the AngLegs making some discoveries about combinations that worked and those that would not. We discussed, without naming it yet, the triangle inequality theorem to explain why some combos did not work. But the real fun, and the clever heart of my colleague’s activity, was when I asked one student from each group to come to the front of the room. When they left their group the remaining group members were given the following task – I slightly modified the original document on the fly – I asked them to make and measure a triangle. Find six measures, the three side lengths and the three angles. They then put the triangle away where it could not be seen. I sent the volunteers back and their teammate gave them three pieces of information. I left it to each group to decide what information to share. Once given three clues the volunteer student needed to manipulate the AngLegs to copy the triangle described. What ensued was a terrific conversation about what information is necessary to guarantee that I have to make the same triangle. We used this as a launching pad to discuss congruence theorems for triangles. I have some great links in the text to some wonderful GeoGebra activities up on the GeoGebraTube site but I know that many of my students do not do these explorations.  I also know that some just need to get their hands dirty, so to speak. Some kids were able to recreate the triangle but admitted that it was a bit of luck. Some stumbled upon the ambiguous case of the Law of Sines without being told that this is what happened. Some realized that they had no choice but to create the correct triangle.

I was really pleased by the level of engagement and I am now thinking about ways to use the AngLeg sets again soon when we start talking about side and angle bisectors. I want to have tables create and draw their own triangles before we stumble into discoveries about concurrence of these bisectors. This will feel, I hope, a little more authentic than me just giving them a prescribed triangle which may feel a bit like I am just luring them into some pre-prepared trap. I think that this activity we ran benefited my students and we have referred to it on a number of occasions already. The grouping of three or four students together at a time helps and allowing them to get their hands busy has helped. Looking forward to loosening up a bit more and letting my students be more tactile in their approach to Geometry. I’ll still show them the GeoGebra and introduce them to Euclid the Game  but I need to remind myself that they are not a bunch of mini Dardys in the room.