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.

To submit to the site, email me at

Also, we tag everything, so check out the bottom of the page for the labels. In a year we’ll have amassed and tagged hundreds of math mistakes, so this site will become a valuable resource for planning lessons.

Enjoy! Be in touch if you have any comments or suggestions.