Web site used in math class-lots of topics/grade levels http://nlvm.usu.edu/en/nav/vlibrary.html
Play some interesting math games http://pbskids.org/cyberchase/games.html
National Geographic for Kids http://www.nationalgeographic.com/kids/
Short articles on science http://www.sciencenewsforkids.org
NASA site with links to areas for students http://www.nasa.gov
Learn about the elements http://chem4kids.com
Learn about volcanoes http://volcano.und.edu
Animal information http://seaworld.org
Learn about energy http://www.eia.doe.gov/kids/
Learn about minerals http://www.theimage.com/mineral/minerals1.html