Topic A begins with students exploring concepts about the ruler. In Lesson 1, they relate length to physical units, by measuring various objects with multiple centimeter cubes. Students create a mental benchmark for the centimeter. In Lesson 2, they apply their knowledge of using centimeter cubes to measure by moving from repeated physical units to iteration of one physical unit. This enables them to internalize their understanding of a length unit as the amount of space between one end of the cube to the other (or space between hash marks). Thus, they begin moving from the concrete to the conceptual. Finally, in Lesson 3, they apply knowledge of known measurements to create unit rulers using one centimeter cube. This deepens the understanding of distance on a ruler and the ruler as a number line.
Grade 2 Mathematics Module 2, Topic A
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