# Clip 6/18: Lesson: Classifying Triangles Part 1C

## Overview Download Transcript (PDF)

Continuing the formative re-engagement lesson on classifying triangles, Hillary Lewis gives the fourth-grade students another example of “another student’s” thinking.

She challenges them to consider “What did the student understand?,” and “What did they get mixed up? Or maybe they didn't understand anything, or maybe they understood everything and didn't get mixed up.”

Some students agree with each other’s ideas, some disagree. All students explain and defend their reasoning, incorporating mathematical and categorical vocabulary as they do so. Lewis challenges them to convince each other in their sharing.

## Teacher Commentary

**
Hillary Lewis
**

I stole this language from award-winning elementary school teacher Mia Buljan: "Convince yourself, convince a friend, and convince a skeptic." I didn't use that in my classroom when I was teaching before, but I totally wanted to use that this year: The idea of, you first have to convince yourself, because we often have that feeling of, I think I'm on the right track, and I'm not exactly sure; and sometimes talking to somebody else either convinces you that you're right, or you find your mistake as you're working through it, or find that you're not on the right track.

Then, convincing a friend, somebody who maybe you both came up with the same answer, and you're talking about your different strategies to the same answer — that would be my idea of convincing a friend.

Lastly, convincing a skeptic, somebody who is thinking very differently from you. I think that's really important to solidify your own thinking.