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4th Grade Math – Classifying Triangles

Clip 8/18: Lesson Part 1E

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Seizing on a moment when a student commented that, when a triangle is rotated, it became clearer that it was obtuse, Hillary Lewis challenges the students to turn-and-talk with a partner to explore their classmate’s idea. 

One student observes that “They probably just forgot that if you turned it more that way or this way, it would be an acute or obtuse, but then if you flip it to its normal form, it would be obtuse.”

Another disagrees, saying, “Even if you flop the triangle, the angle will keep the same. The angle will stay the same. It's the same triangle, you're just putting it different ways to look. It's the same triangle. So, if we figure that that is obtuse, any way you swap it, it’s going to be still obtuse. There's no way you can swap an obtuse into an acute triangle, because they're totally different.”

Teacher Commentary

Hillary Lewis

The students engaged with each other well and used really nice — I don't know if they were sentence stems, but they would bond by saying, "To build on what so-and-so was saying …”

That was a really nice way to connect and show that they were listening to each other and building on each other. That was a gift, and I had nothing to do with that. Their classroom teacher did that, but because of the lesson — the way I designed the lesson — it needed that kind of conversation, and so it worked. It worked really well.