1.)Place students into groups of two.
2.)Ask the pairs to build as many different rectangles as possible using 12 tiles.
3.)Walk around answering questions that arise. Some students will try building rectangles using twelve tiles as an outside perimeter. Be sure to explain that the rectangular arrays must have no holes in the middle.
4.)Have different groups share their findings. (3x4, 6x2, and 12x1)
5.)Have students draw their rectangles on graph paper and list their factor pairs for each rectangular array.
6.)Give students at least two more composite numbers to build, share and draw.
7.)Give students the number 7 and ask them to build as many possible rectangles using only 7 tiles.
8.)Discuss how their is only one rectangle that can be built using 7 tiles (7x1 or 1x7).
9.)Give students another prime number and ask them to build and graph as many rectangles as possible.
10.)When students realize that once again their is only one rectangle possible share with them that this is because these are special numbers we call prime numbers.
11.)Display a hundreds chart on an Interactive White Board (see link). Allow groups to come to the front and shade the prime numbers they found and share their strategy for finding the primes.
)This site offers lessons using the hundreds chart and also a blank template of the hundreds chart.