# Clip 3/18: Pre-Lesson: Classifying Triangles Part 3

## Overview Download Transcript (PDF)

Hillary Lewis and her lesson study collaborators discuss what they anticipate the students will do in engaging the concepts of that day’s lesson, and the steps of the lesson.

Hillary shares that she will begin with a poster of triangles and ask the students to regenerate their definitions. She then will share two triangle models with errors and ask the students to reflect on and improve the students’ thinking in these examples.

## Teacher Commentary

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Hillary Lewis

Our topic of conversation was, Where do we go from the week before with triangle categorization? And that's when we decided that, rather than just identifying pre-existing triangles, they needed to construct the triangles themselves, and be able to identify, “Okay, I created a right isosceles triangle,” and so forth.

Rather than just having a blank piece of paper, and having them construct, we decided having the geometric figures already on the paper would be maybe a little more interesting and engaging to begin with, but also pose its own challenge as, How are you going to draw those lines and use the lines that are already there? Is there already a right angle there? Are you going to use it, or are you going to split it up?