Perimeter of Regular and Irregular Shapes

Perimeter in Grade 4 is formalized: it is the sum of all side lengths. For regular polygons, this simplifies to n x side length. For irregular polygons, every side must be measured and added. The geoboard is the ideal tool because it allows students to build shapes, adjust them, and measure simultaneously. Perimeter has immediate practical applications: fencing a garden, framing a picture, bordering a floor.