Find the area of a rectangle by counting unit squares. This builds on the ability to skip-count.
Next, give your students this challenge:
Cut each of the following figures into four pieces, with each piece being the same shape and size.

Cut each of the following figures into five pieces, with each piece being the same shape and size.

Conclude by leading this investigation:
Earth Attack – addition puzzle
by MathPickle
2.G.A.2: Partition a rectangle into rows and columns of same-size squares and count to find the total number of them.