The teacher is expanding students’ flexibility by having them do another, similar subtraction problem, but this time having them compare two representations of the problem. The round number in the previous problem was 20; this time it’s 30. The student is able to explain that a round number, which he calls an easy number, can be in tens, hundreds, or thousands, demonstrating the flexible thinking the teacher is after. Many students learn a mathematics procedure, but when they are given a problem that uses the same mathematics but looks different, they are stuck. This student is demonstrating mastery of the idea of getting to the round number, regardless of the number of zeros.

Notice that the teacher listens in and identifies students who understand the answer. She lets them know she is going to call on them so they can practice articulating their answer. In this segment, the student is able to rehearse what she will say twice. When the teacher calls on her, she is able to explain clearly. This is a helpful move because students will be best able to understand one of their peers if that peer can articulate clearly. The teacher calls on others to restate the answer so that, even if some students were not initially clear, they have the opportunity to explain based on the explanation of the student who modeled.