Clip 9/29: Day 1: Decimal Lesson Part D

Overview

In the second documented day of the learning segment, Erika Isomura begins with a number talk with her 5th-grade students, noticing how and why divisors get smaller. Her students share their thoughts (e.g., “divide by 10 each time”), and they note that the quotient is getting bigger each time by 10.

In a number talk, Erika responds to a student’s wondering on the previous day about what happens if you work with a different number — for example, 2,300/100. Erika uses patterns suggested by the students themselves (e.g. “Yeini’s pattern”) to reduce by a power of 10 or increase by a power of 10 (e.g., 2,300/.001).

Teacher Commentary

The purpose of this lesson was to let my students see decimals. They had been working with mostly dividing, although some multiplying where fractions were ... I don't know if they're called this, but I call them decimal fractions in here. Denominators of tens, hundreds, thousands and so on. The number talks have been working with those type of fractions. I wanted them to see problems that look similar to what we had done on our number strings, but then the answer looked different because we had done it in a calculator.

In the week before, my students were puzzling with this idea, but then they did think they saw it. They were really pushing that, and that's such a huge thing, the idea of “if it's small divided by big, you will have a fractional result.”

I wanted to make sure that they got that solid because that was something that could be used for later work when we do estimation. When they see a problem they're like, "Obviously it can't be this or obviously it has to be greater than a whole, because…."