Description: One of a series of documents describing the progression of a topic across several grade levels, informed both by research on children's development and by the structure of mathematics. Third graders focus on solving real-world and mathematical problems involving perimeters of polygons. Solve real world and mathematical problems involving perimeters of polygons, including finding the perimeter given the side lengths, finding an unknown side length, and exhibiting rectangles with the same perimeter and different areas or with the same area and different perimeters. Next, students learn to mark off unit lengths with a ruler and label the length of each side of the polygon.*Teacher Advisor is 100% free.