Site Business

Global Math Department, 9 PM

I’m holding on to today’s post. The grand reveal will be tonight, at the meeting of the Global Math Department, 9 PM.

The talk is going to be about the site. Quick preview: I’m going to argue that there are some important ways in which this experiment hasn’t lived up to my/our expectations. I’m also going to suggest a new direction for the site, which I’ll try to kick off tonight.

I’m worried that my analysis is going to be way off, but check it out. I’ll try to say stuff that might be right, and hopefully more people will be tempted to contribute to the site.

Thanks for all of your contributions to the site so far. This thing is great, and you all built it.

Site Business

Call for submissions

If you find yourself around kids on a regular basis, consider putting math problems in front of them. Consider collecting those math problems, and taking a picture* of the ones that they mess up. If you do all that, and send it in to me, we’ll help build a database of student work that is unparalleled. It will be of immense use to students and teachers.

Send the messages to We’ll send you a thank you note, and a free subscription to the Math Mistakes website.**


*If you don’t feel comfortable taking pictures of student work, or if your district has rules forbidding it, then consider taking a second to copy down their work and sending it in. 

** That’s a joke.

Site Business

Call for feedback: Categories

Hey everyone. The way that I’m categorizing mistakes isn’t really working for me, and I’m curious what all you users of the site think about what we’ve been doing.

Here are my questions:

  1. Suppose that I stopped categorizing posts by CCSS standard (i.e. “A.REI.3”) and instead used the CCSS categories (i.e. “High School – Algebra – Reasoning about equations and inequalities”). Would that bug you? Anybody out there really like the categorizing by standard?
  2. Right now I categorize posts in two different ways. First, by topic and course (i.e. “Algebra 1, Inequalities”) and also by CCSS. Let’s say that I told you that I was going to just do the CCSS stuff. Would that make you happy/sad/morose/nonplussed, or would that have no impact in your life?

I’m looking for feedback. Please leave a few quick thoughts in the comments of this post.

(Also, feel free to start a more general conversation about features of the site.)

Site Business

Call for submissions

Hey everybody,

One of the best ways to support this project is to submit some student work. We’ve got about another week worth of student work before we run out, so if you enjoy this site I’d like to encourage you to submit.  A couple of things about submitting work to the site:

  • Some people aren’t allowed to share original student work. You can still share, though, if you just copy or type out the student’s work. We’ll post that.
  • Once school starts, I’m going to just have a camera with me every time that I grade. When I see something interesting or representative of a common error, I’m going to snap a quick picture of it. It would be great if a lot of you would do the same.
  • I also post other sources of student errors. So if you’re watching a video on youtube, reading an article with some good samples of student thinking, or looking through the Q&A section of  a Khan Academy video, feel free to submit those too. Really, anything that represents mathematical thought is fair game for the site.

Thank you for all of your support so far. Your submissions and comments are already making this site a really valuable tool for a lot of people. Great work, gang! Let’s keep it up.


Site Business

Open thread for feedback

It’s the Math Mistakes 3 week (or so) anniversary!

I’m opening this thread for feedback on the site.  In the comments, tell us what you like. More importantly, tell us what you don’t like so that we can get better.

Here are some things that I’d like to hear about:

  • The look of the new site
  • The quality of the mistakes that are posted
  • The experience of analyzing the mistakes — do you find it challenging, or is it easy to understand and respond to a student error?
  • The quality of the prompting questions in the posts
  • The ability to browse mistakes using the menu on the left
I’ll end the post with a quick plug to send us your or your students’ mistakes. If you find yourself going back to school, remember to bring a camera and find 4-5 interesting errors to send in. Especially if you teach K-8 or college math.
Site Business

The idea

Here’s the idea for this site:

Teachers need to be able to quickly look at mathematical work and identify the assumptions behind the work, and what actions to take in response to the work. That’s hard. But practice can help us get better at this.

The idea is that on this site each post will be a selection of student work. That student work will be posted by me, but sent in by you. And then in the comments we’ll discuss: what are the assumptions behind this work, and what could the next steps be.