All about Shapes

The third grade recently wrapped up a unit on area, perimeter, and 2-D geometry. This unit helps lay the groundwork for future geometric thinking in middle school and beyond.

Students began the investigation by defining what perimeter and area are. Earlier in the year third graders had practiced measuring and were familiar with units like feet, centimeters, meters, and inches. In the first semester they learned to accurately measure distances in both the metric system and imperial system (commonly called “U.S. standard in our curriculum).

This unit expanded upon the idea by asking students to consider how to measure the outside of a shape with many sides. These exercises helped students build an understanding that perimeter was the total measurement of the outside edges of a shape. After this students began to explore the idea of area, or measuring the space inside the shape. This lead to further considerations about what units were appropriate when describing how much surface a shape had.

Students began to notice interesting relationships between area and perimeter over the course of the study. Classes were surprised to learn that shapes with relatively large perimeters could have small areas or that shapes with different perimeters could in fact have the same area!

The unit closed with a deep dive into 2-D shapes. Students learned to define various triangles and quadrilaterals based on number of sides, angles, types of angles, and the relationship of the sides. Classes noted that shapes they once thought as simple could have lots of variations and very particular definitions. The relationship between squares, rhombuses, and rectangles is a particularly interesting one.