Paul Salomon’s “imbalance problems”. You know how I love a thought-provoking picture.
Sh*t I F*cking Love (Wherein I Am Moved to Profanity by Enthusiasm) Friday, Apr 5 2013
Deborah Ball and Lucy West are F*cking Masters Sunday, Mar 31 2013
I recently saw some video from Deborah Ball’s Elementary Mathematics Laboratory. I actually didn’t know what she looked like so I didn’t find out till afterward that the teacher in the video was, y’know, THE Deborah Ball, but already from watching, I was thinking,
THAT IS A F*CKING MASTER. I F*CKING LOVE HER.
It put me in mind of a professional development workshop I attended 2 years ago which was run by Lucy West. Both Ball and West displayed a level of adeptness at getting students to engage with one another’s reasoning that blew me away.
One trick both of them used was to consistently ask students to summarize one another’s train of thought. This set up a classroom norm that you are expected to follow and be able to recapitulate the last thoughts that were said, no matter who they are coming from. Both Ball and West explicitly articulated this norm as well as implicitly backing it up by asking students (or in West’s case, teachers in a professional development setting) to do it all the time. In both cases, the effect was immediate and powerful: everybody was paying attention to everybody else.
The benefit wasn’t just from a management standpoint. There’s something both very democratic and very mathematically sound about this. In the first place, it says that everybody’s thoughts matter. In the second, it says that reasoning is the heart of what we’re doing here.
I resolve to start employing this technique whenever I have classroom opportunities. I know that it’ll come out choppy at first, but I’ve seen the payoff and it’s worth it.
A nuance of the technique is to distinguish summarizing from evaluating. In the Ball video, the first student to summarize what another student said also wanted to say why he thought it was wrong; Ball intercepted this and kept him focused on articulating the reasoning, saving the evaluation step until after the original train of thought had been clearly explicated. Which brings me to a second beautiful thing she did.
Here was the problem:
The first student to speak argued that the blue triangle represents half because there are two equal wholes in the little rectangle at the top right.
He is, of course, wrong.
On the other hand, he is also, of course, onto something.
It was with breathtaking deftness that Deborah Ball proceeded to facilitate a conversation that both
(a) clearly acknowledged the sound reasoning behind his answer
(b) clarified that he missed something key.
It went something like this. I’m reconstructing this from memory so of course it’s wrong in the details, but in overall outline this is what happened –
Ball: Who can summarize what [Kid A] said?
Kid B: He said it’s half, but he’s just looking at the, he’s just…
Ball: It’s not time to say what you think of his reasoning yet, first we have to understand what he said.
Kid B: Oh.
Kid C: He’s saying that the little rectangle has 2 equal parts and the blue is one of them.
Ball [to Kid A]: Is that what you’re saying?
Kid A: Yeah.
Ball: So, what was the whole you were looking at?
Kid A [points to the smaller rectangle in the upper right hand corner]
Ball: And what were the two parts?
Kid A [points to the blue triangle and its complement in the smaller rectangle]
Ball: And are they equal?
Kid A: Yes.
Ball [to the rest of the class]: So if this is the whole [pointing at the smaller rectangle Kid A highlighted], is he right that it’s 1/2?
Many students: Yes.
Ball: The question was asking something a little different from that. Who can say what the whole in the question was?
Kid D [comes to the board and outlines the large rectangle with her finger]
Kid A: Oh.
I loved this. This is how you do it! Right reasoning has been brought to the fore, wrong reasoning has been brought to the fore, nobody feels dumb, and the class stays focused on trying to understand, which is what matters anyway.
Good Brawls and Honoring Kids’ Dissatisfaction Friday, Mar 8 2013
I was just reading some old correspondence with a friend J who periodically writes me regarding a math question he and his son are pondering together. The exchange was pretty juicy, about how many ways can an even number be decomposed as a sum of primes. But actually, the juiciest thing we got into was this:
Is 1 a prime number?
It was kind of a fight! Since I and Wikipedia agreed on this point (it’s not prime), J acknowledged we must know something he didn’t. But regardless, he kind of wasn’t having it.
Point 1: This is awesome.
Nothing could be better mathematician training than a fight about math. Proofs are called “arguments” for a reason.
When I went to Bob and Ellen Kaplan’s math circle training in 2009, I was heading to do a practice math circle with some high schoolers and Bob asked me, “what question are you opening with?” I said, “does .9999…=1?” He smiled with knowing anticipation and said, “oooh, that one always starts a brawl.”
Well, it wasn’t quite the bloodbath Bob led me to expect, but the kids were totally divided. One kid knew the “proof” where you go
Multiplying by 10,
and the other kids had that same sort of feeling like, “he knows something we don’t know,” but they weren’t convinced, and with only a minimal amount coaxing, they weren’t shy about it. The resulting conversation was the stuff of real growth: everybody in the room was contending with, and thereby pushing, the limits of their understanding. Even the boy who “knew the right answer” began to realize he didn’t have the whole story, as he found himself struggling to be articulate in the face of his classmates’ doubt.
Now this could have gone a completely different way. It’s common for “0.999… = 1″ to be treated as a fact and the above as a proof. Similarly, since the Wikipedia entry on prime numbers says, “… a natural number greater than 1 that has no positive divisors…,” we could just leave it at that.
But in both situations, this would be to dishonor everyone’s dissatisfaction. It is so vital that we honor it. Everybody, school-aged through grown-up, is constantly walking away from math thinking “I don’t get it.” This is a useless perspective. Never let them say they don’t get it. What they should be thinking is that they don’t buy it.
And they shouldn’t! If it wasn’t already clear that I think the above “proof” that 0.999…=1 is bullsh*t, let me make it clear. I think that argument, presented as proof, is dishonest.
I mean, if you understand real analysis, I have no beef with it. But at the level where this conversation is usually happening, this is not a proof, are you kidding me?? THE LEFT SIDE IS AN INFINITE SERIES. That means to make this argument sound, you have to deal with everything that is involved with understanding infinite series! But you just kinda slipped that in the back door, and nobody said anything because they are not used to honoring their dissatisfaction. As I have pointed out in the past, if you ignore all the series convergence issues, the exact same argument proves that …999.0=-1:
Dividing by 10,
If you smell a rat, good! My point is that that same rat is smelling up the other proof too. We need to have some respect for kids’ minds when they look funny at you when you tell them 0.999…=1. They should be looking at you funny!
Same thing with why 1 is not a prime. If a student feels like 1 should be prime, that deserves some frickin respect! Because they are behaving like a mathematician! Definitions don’t get dropped down from the sky; they take their form by mathematicians arguing about them. And they get tweaked as our understanding evolves. People were still arguing about whether 1 was prime as late as the 19th century. Today, no number theorist thinks 1 is prime; however, in the 20th century we discovered a connection between primes and valuations, which has led to the idea in algebraic number theory that in addition to the ordinary primes there is an “infinite” prime, corresponding to the ordinary absolute value just as each ordinary prime corresponds to a p-adic absolute value. Now for goodness sakes, I hope you don’t buy this! With study, I have gained some sense of the utility of the idea, but I’m not entirely sold myself.
To summarize, point 2: Change “I don’t get it” to “I don’t buy it”.
Now I think this change is a good idea for everyone learning mathematics, at any level but especially in school, and I think we should teach kids to change their thinking in this way regardless of what they’re working on. But there is something special to me about these two questions (is 0.999…=1? Is 1 prime?) that bring this idea to the foreground. They’re like custom-made to start a fight. If you raise these questions with students and you are intellectually honest with them and encourage them to be honest with you, you are guaranteed to find that many of them will not buy the “right answers.” What is special about these questions?
I think it’s that the “right answers” are determined by considerations that are coming from parts of math way beyond the level where the conversation is happening. As noted above, the “full story” on 0.999…=1, in fact, the full story on the left side even having meaning, involves real analysis. We tend to slip infinite decimals sideways into the grade-school/middle-school curriculum without comment, kind of like, “oh, you know, kids, 0.3333…. is just like 0.3 or 0.33 but with more 3’s!” Students are uncomfortable with this, but we just squoosh their discomfort by ignoring it and acting perfectly comfortable ourselves, and eventually they get used to the idea and forget that they were ever uncomfortable.
Meanwhile, the full story on whether 1 is prime involves the full story on what a prime is. As above, that’s a story that even at the level of PhD study I don’t feel I fully have yet. The more I learn the more convinced I am that it would be wrong to say 1 is prime; but the learning is the point. If you tell them “a prime is a number whose only divisors are 1 and itself,” well, then, 1 is prime! Changing the definition to “exactly 2 factors” can feel like a contrivance to kick out 1 unfairly. It’s not until you get into heavier stuff (e.g. if 1 is prime, then prime factorizations aren’t unique) that it begins to feel wrong to lump 1 in with the others.
I highlight this because it means that trying to wrap up these questions with pat answers, like the phony proof above that 0.999…=1, is dishonest. Serious questions are being swept under the rug. The flip side is that really honoring students’ dissatisfaction is a way into this heavier stuff! It’s a win-win. I would love to have a big catalogue of questions like these: 3- to 6-word questions you could pose at the K-8 level but you still feel like you’re learning something about in grad school. Got any more for me?
All this puts me in mind of a beautiful 15-minute digression I witnessed about 2 years ago in the middle of Jesse Johnson’s class regarding the question is zero even or odd? It wasn’t on the lesson plan, but when it came up, Jesse gave it the full floor, and let me tell you it was gorgeous. A lot of kids wanted the answer to be that 0 is neither even nor odd; but a handful of kids, led by a particularly intrepid, diminutive boy, grew convinced that it is even. Watching him struggle to form his thoughts into an articulate point for others, and watching them contend with those thoughts, was like watching brains grow bigger visibly in real time.
Honor your dissatisfaction. Honor their dissatisfaction. Math was made for an honest fight.
p.s. Obliquely relevant: Teach the Controversy (Dan Meyer)
A Note to My Fellow White People Friday, Jan 18 2013
I haven’t talked openly about race or racial difference on this blog before, but I actually think about it a lot. One of the most damning legacies of our racist history has been systematic libel against the minds of black and brown children (and adults for that matter). Meanwhile, in our culture, math is the ultimate signifier of intelligence. So the math classroom has heightened power, both to inflict injustice and to rectify it. Given this, plus the diversity of teachers and students, a comfortable cross-race conversation about racial matters is a must for the profession. In the spirit of contributing to that conversation, I offer
A Note to My Fellow White People
Guys, we have to chill out a little. It has to be possible for somebody to say to you, “that was ignorant,” or “that was racially offensive,” or even “that was racist,” without you flipping out, getting offended or defensive, or needing to be reassured you are not a horrible person. It’s not a good look, on any level: it’s not dignified, and it makes it impossible to have a productive conversation about race across racial lines.
I was at a cafe a couple months back trying to get some schoolwork done when I found myself distracted by a profoundly uncomfortable conversation at the next table. There was a white man in his early 50s and two black women, one close to his age and one closer to mine. They seemed to be sharing a familiar and friendly meal. Things started to go south when the man admitted to being afraid of a young black man on the street. The younger of the women said something to the effect of, “you might have work to do on that.”
Her tone was warm: she wasn’t being accusatory but rather seemed to be offering her words in the spirit of holding her friend to a high standard. But the man immediately became anxious, although his face and words were all smiles and jokes. His first response was that white people make him more uncomfortable than black people, as though he could re-establish his lost racial coolness with sufficiently loud declamations of prejudice against white people.
The women weren’t having it. “You’re being ignorant against white people now.” I interpreted their response as saying, “you can’t get off the hook with this diversionary tactic.” But he kept trying. His anxiety was as audible to me as a fire alarm, even when he wasn’t talking. I tried to concentrate on my math but I couldn’t get anything done.
Things stayed in this state, a tense, anxious impasse overlaid by a thin layer of too-eager conviviality and jokes, for about 20 minutes, till they got up to leave, no noticeable progress having been made in the conversation. At this point the man, in that same overly-eager joking tone, almost-but-not-quite-explicitly asked for reassurance that everybody was still his friend. They gave him the reassurance. On their way out, the younger woman leaned over to my table and apologized for her “ignorant friend.”
I’m not telling you this story to put the man down or call him ignorant. I don’t remember the context of the conversation and I don’t have my own opinion about it. Also, I think in all likelihood he’s a completely nice and decent person, and so are the women.
The point of the story is the man’s intense anxiety at being put on the spot racially, and the way that anxiety dominated both the conversation and its goals (so that what started as an attempt to raise consciousness was aborted, and turned into a reassurance fest), and the social and public space (so that the younger woman felt the need to apologize to a neighboring table).
Now I don’t fail to have empathy for him. If you are a white person with a modicum of sense and decency, you know that you are the beneficiary of an unjust history. (Shout out to Louis CK.) Just knowing that you’re benefiting is already a little uncomfortable to begin with. Feeling like you might be participating in that injustice can make the discomfort acute. I’ve been there many times.
But, guys, we’ve got to get it together! It is necessary to learn how to be with that discomfort and still function. First of all, the story I just told you is about a grown-a** man! Trying to prove how un-racist you are, and then needing to be coddled and preened so that you know the trouble is past, is unbefitting of the dignity of an adult. So is any other response aimed at removing the source of your discomfort rather than tolerating it – throwing a fit, acting defensive or offended, etc. Shouldn’t we aspire to some grace here?
Secondly, it makes it impossible for the conversation to advance! If we want to avoid participating in injustice we have to be willing to tolerate the possibility that we already are participating. Otherwise how will we learn what to avoid? In the anecdote I’ve recounted here, the man’s anxiety shut down the ability of the conversation to make any progress. He was blessed with friends who were willing to hold him to a higher standard and he was too busy freaking out to get the benefit of that! The bottom line question is, would you rather spend your time and energy proving how un-racist you are, or would you actually like to learn how to make the world better?
All of this puts me in mind of a much more public incident. In 2009, Attorney General Eric Holder gave a speech at the Dept. of Justice Black History Month program in which he said that Americans are afraid to talk about race and called upon us to do better. Multiple commentators immediately jumped down his throat.
Thereby proving his point.
The Attorney General made an effort to hold the nation to a higher standard. At the time, we didn’t react with grace or manifest any interest in growing.
How about now?
IMO the best thing white teachers, or any teachers who find themselves teaching classes of black/brown students can do is to constantly hold their students to the same high standards they would hold their own biological children to. Giving these kids a high standard education is one of the few ways to equip these kids to deal with racism.
Notes from the Learning Lab: How to Dull My Curiosity Friday, Dec 14 2012
I know I say this kind of thing a lot but I’m sitting here studying for a final, and this truth is just glaring and throbbing at me:
If you want to dull my curiosity, tell me what the answer is supposed to be.
If you want to make my curiosity vanish completely, do that and then add in a little time pressure.
There is nothing as lethal to my sense of wonder as that alchemical combination of already knowing how things are going to turn out (without knowing why), and feeling the clock tick.
Wherein This Blog Serves Its Original Function Wednesday, Nov 21 2012
The original inspiration for starting this blog was the following:
I read research articles and other writing on math education (and education more generally) when I can. I had been fantasizing (back in fall 2009) about keeping an annotated bibliography of articles I read, to defeat the feeling that I couldn’t remember what was in them a few months later. However, this is one of those virtuous side projects that I never seemed to get to. I had also met Kate Nowak and Jesse Johnson at a conference that summer, and due to Kate’s inspiration, Jesse had started blogging. The two ideas came together and clicked: I could keep my annotated bibliography as a blog, and then it would be more exciting and motivating.
That’s how I started, but while I’ve occasionally engaged in lengthy explication and analysis of a single piece of writing, this blog has never really been an annotated bibliography. EXCEPT FOR RIGHT THIS VERY SECOND. HA! Take THAT, Mr. Things-Never-Go-According-To-Plan Monster!
“Opportunities to Learn Reasoning and Proof in High School Mathematics Textbooks”, by Denisse R. Thompson, Sharon L. Senk, and Gwendolyn J. Johnson, published in the Journal for Research in Mathematics Education, Vol. 43 No. 3, May 2012, pp. 253-295
The authors looked at HS level textbooks from six series (Key Curriculum Press; Core Plus; UCSMP; and divisions of the major publishers Holt, Glencoe, and Prentice-Hall) and analyzed the lessons and problem sets from the point of view of “what are the opportunities to learn about proof?” To keep the project manageable they just looked at Alg. 1, Alg. 2 and Precalc books and focused on the lessons on exponents, logarithms and polynomials.
They cast the net wide, looking for any “proof-related reasoning,” not just actual proofs. For lessons, they were looking for any justification of stated results: either an actual proof, or a specific example that illustrated the method of the general argument, or an opportunity for students to fill in the argument. For exercise sets, they looked at problems that asked students to make or investigate a conjecture or evaluate an argument or find a mistake in an argument in addition to asking students to actually develop an argument.
In spite of this wide net, they found that:
* In the exposition, proof-related reasoning is common but lack of justification is equally common: across the textbook series, 40% of the mathematical assertions about the chosen topics were made without any form of justification;
* In the exercises, proof-related reasoning was exceedingly rare: across the textbook series, less than 6% of exercises involved any proof-related reasoning. Only 3% involved actually making or evaluating an argument.
* Core Plus had the greatest percentage of exercises with opportunities for students to develop an argument (7.5%), and also to engage in proof-related reasoning more generally (14.7%). Glencoe had the least (1.7% and 3.5% respectively). Key Curriculum Press had the greatest percentage of exercises with opportunities for students to make a conjecture (6.0%). Holt had the least (1.2%).
The authors conclude that mainstream curricular materials do not reflect the pride of place given to reasoning and proof in the education research literature and in curricular mandates.
“Expert and Novice Approaches to Reading Mathematical Proofs”, by Matthew Inglis and Lara Alcock, published in the Journal for Research in Mathematics Education, Vol. 43 No. 4, July 2012, pp. 358-390
The authors had groups of undergraduates and research mathematicians read several short, student-work-typed proofs of elementary theorems, and decide if the proofs were valid. They taped the participants’ eye movements to see where their attention was directed.
* The mathematicians did not have uniform agreement on the validity of the proofs. Some of the proofs had a clear mistake and then the mathematicians did agree, but others were more ambiguous. (The proofs that were used are in an appendix in the article so you can have a look for yourself if you have JSTOR or whatever.) The authors are interested in using this result to challenge the conventional wisdom that mathematicians have a strong shared standard for judging proofs. I am sympathetic to the project of recognizing the way that proof reading depends on context, but found this argument a little irritating. The proofs used by the authors look like student work: the sequence of ideas isn’t being communicated clearly. So it wasn’t the validity of a sequence of ideas that the participants evaluated, it was also the success of an imperfect attempt to communicate that sequence. Maybe this distinction is ultimately unsupportable, but I think it has to be acknowledged in order to give the idea that mathematicians have high levels of agreement about proofs its due. Nobody who espouses this really thinks that mathematicians are likely to agree on what counts as clear communication. Somehow the sequence of ideas has to be separated from the attempt to communicate it if this idea is to be legitimately tested.
* The undergraduates spent a higher percentage of the time looking at the formulas in the proofs and a lower percentage of time looking at the text, as compared with the mathematicians. The authors argue that this is not fully explained by the hypothesis that the students had more trouble processing the formulas, since the undergrads spent only slightly more time total on them. The mathematicians spent substantially more time on the text. The authors speculate that the students were not paying as much attention to the logic of the arguments, and that this pattern accounts for some of the notorious difficulty that students have in determining the validity of proofs.
* The mathematicians moved their focus back and forth between consecutive lines of the proofs more frequently than the undergrads did. The authors suggest that the mathematicians were doing this to try to infer the “implicit warrant” that justified the 2nd line from the 1st.
The authors are also interested in arguing that mathematicians’ introspective descriptions of their proof-validation behavior are not reliable. Their evidence is that previous research (Weber, 2008: “How mathematicians determine if an argument is a valid proof”, JRME 39, pp. 431-459) based on introspective descriptions of mathematicians found that mathematicians begin by reading quickly through a proof to get the overall structure, before going into the details; however, none of the mathematicians in the present study did this according to their eye data. One of them stated that she does this in her informal debrief after the study, but her eye data didn’t indicate that she did it here. Again I’m sympathetic to the project of shaking up conventional wisdom, and there is lots of research in other fields to suggest that experts are not generally expert at describing their expert behavior, and I think it’s great when we (mathematicians or anyone else) have it pointed out to us that we aren’t right about everything. But I don’t feel the authors have quite got the smoking gun they claim to have. As they acknowledge in the study, the proofs they used are all really short. These aren’t the proofs to test the quick-read-thru hypothesis on.
The authors conclude by suggesting that when attempting to teach students how to read proofs, it might be useful to explicitly teach them to mimic the major difference found between novices and experts in the study: in particular, the idea is to teach them to ask themselves if a “warrant” is required to get from one line to the next, to try to come up with one if it is, and then to evaluate it. This idea seems interesting to me, especially in any class where students are expected to read a text containing proofs. (The authors are also calling for research that tests the efficacy of this idea.)
The authors also suggest ways that proof-writing could be changed to make it easier for non-experts to determine validity. They suggest (a) reducing the amount of symbolism to prevent students being distracted by it, and (b) making the between-line warrants more explicit. These ideas strike me as ridiculous. Texts already differ dramatically with respect to (a) and (b), there is no systemic platform from which to influence proof-writing anyway, and in any case as the authors rightly note, there are also costs to both, so the sweet spot in terms of text / symbolism balance isn’t at all clear and neither is the implicit / explicit balance. Maybe I’m being mean.
Thurston Monday, Aug 27 2012
I got home last night from a week and a half of traveling to find a newspaper clipping my mother sent me: the obituary for Bill Thurston in the New York Times. I hadn’t know he was sick.
Thurston was a giant of twentieth century geometry, but more important to me is the sense I always get from his writing – a sense of warmth, the intention to share, an abiding interest in math as a human practice. A complete lack of interest in the privilege of being seen as brilliant. A desire to demystify the process of mathematical discovery.
I spent some time today looking for online tributes. Justin Lanier wrote a beautiful one. My desire to refer you to this was the impulse that prompted this post.
Here’s something else beautiful: Thurston’s profile on MathOverflow, linking to the questions he asked and answered on that site.
And for math and art enthusiasts, here’s some high fashion inspired by Thurston’s work.
Rest in peace Bill Thurston.