http://www.eecs.umich.edu/mathscience

This is a great site for all sorts of K-12 science lessons and experiments. The lessons are grouped by subject and grade level. Many are set up to answer questions, like “Why does my voice sound different on a tape recorder?” or “How does a bicycle and its rider stay upright?” Other highlights include “Fun with Liquid Nitrogen,” where students can make ice cream in minutes using liquid nitrogen, plus cooking with solar energy, making toothpaste, rigging a burglar alarm, and DNA fingerprinting