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9th Grade Math - Modeling through Geometry: Circumference of a Cup’s Roll

Clip 4/19: Modeling through Geometry: Pre-Lesson Part 4


In a pre-lesson conversation, Molly McNinch tells math colleague Jim Karditzas about a pre-assessment she had administered before the lesson shown in these video clips. She talks about what the pre-assessment revealed about students’ “success, or misconceptions, or struggles.” She describes prompting students to model mathematically: “Could you represent this using variables and operations? How would you think about it in a more mathematical way where you can represent it with a model, represent it with all different types of images?" Molly describes her rationale for using a status poster to require students to make their justifications visible.

Teacher Commentary

In the pre-assessment, a lot of my students were able to see the relationship between the wide and narrow diameters — the top and bottom of the cup. And so they knew that there was a relationship there, between the wide diameter specifically and the roll radius. A lot of them discovered that the relationship between the wide and narrow diameters, depending on the difference, is the smaller the difference, the larger the circle. A lot of the students who were struggling, were struggling because they only could get so far.