In their pre-lesson conversation, Molly McNinch is asked by her math colleague Jim Karditzas to describe how the documented lesson fits into her larger unit of study. Molly responds that the larger unit focuses on tessellations and transformations, and the class had just completed a previous unit on similarity.

9th Grade Math - Modeling through Geometry: Circumference of a Cup’s Roll*Molly McNinch, San Lorenzo Unified School District, Woodside High School, Woodside, California*

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MOLLY MCNINCH: So currently, we're working on unit six -- or chapter six, which is regarding tessellations and transformations. Prior to chapter six, we did similarity. So chapter six deals with all the different transformations and how you represent them with ordered pair rules. And chapter seven deals with similarity of triangles and the proportions of the triangle when it's cut by a parallel line. And so this particular lesson ties nicely into chapter seven, which is also going to tie into [chapter] eight. So it sandwiches the chapter six by embedding that similarity piece. And so I think also it really ties nicely because it talks about the proportions of the different triangle measures and the similarity of triangles, which students tend to have slightly more hang-ups with than the congruence of triangles.

And so that's something that -- not a lot of students, but some students will have struggles identifying similarity over congruence and justifying what makes it similar versus what makes it congruent.

Some students will have struggles identifying similarity over congruence. And justifying what makes it similar versus what makes it congruent.