I the same lesson with my 4th graders that twinmom07 explained. The difference is she uses cubes to build arrays and we use grid paper and cut out the arrays. We post the arrays for each number 1-25 on a separate piece of contruction paper and display them. (By the way, each student does NOT do all 25 numbers. Different groups are responsible for cutting out the arrays for certain numbers.) Students label each array with the appropriate expression (or equation if you wish). After all the numbers are displayed around the room -- usually the next day, we go to each number and identify them as prime, composite
based on the number of arrays/factors and square
based on the shape of the array. Students record all this information on a recording sheet much like twinmom07 uses too.
We leave these displays up all year and refer to them frequently. It's always interesting to hear 4th graders refer to numbers as prime because they only have one rectangle! I have to remind them the rectangle's dimensions are the factors. The brains that grade the BIG STATE test at the end of the year won't necessarily know what they mean by, "A prime number has only has one rectangle."
I also like twinmom07's prImE and cOmpOsItE example. I'm adding it to my lessons from now on. You could probably make up (or have your students make up) a song or a chant to go along with the concept.
Right now I'm seeing students squat for the consonants and pop up for the vowels!!!!!
A little kinesthetic sometimes works wonders.