This lesson teaches students how to calculate the area of a parallelogram by decomposing it into rectangles. Students are given a template of a parallelogram and instructed to cut it along a dotted perpendicular line to form a rectangle. By doing this, they see that the area does not change and understand that the area formula for a parallelogram is the same as that of a rectangle: Area = base x height. The lesson provides examples of finding the height, base, and area of various parallelograms and ensures students understand that the height must be drawn perpendicular to the base.