ckcowl's method is by far the easiest and gives a really nice result. Two things important to remember is to secure the muslin squares to something so it will be easy for the kids to color on, and to heat-set the individual squares by first protecting your ironing board cover with sheets of copy paper and then putting a couple of sheets on top and iron on hot, no steam. Let cool, sash and add borders and there you are! Nice quilt for the teacher!
Dana