Ask Dr. Math- http://forum.swarthmore.edu/dr.math/index.html
A great site for students who have math questions. Ask Dr. Math is a question and answer service for K-12 students and their teachers.
Math Magic- http://mathforum.com/mathmagic/
Math magic has an interactive competition for students K-12 from all over the world to take part in. Students can take part in these activities as a team or as a school.
The World of Math Online- http://www.aplusmath.com/
This site has interactive help tools for math as well as lesson plans fro math. There are games and puzzles, interactive homework helpers and worksheets that can be downloaded.
GREAT SITES FOR TEACHERS
I Love Teaching .Com- http://www.iloveteaching.com/index.htm
This is a great site for first year teachers. It has lesson plans as well as ideas and tips for new teachers.
Education Planet- http://www.educationplanet.com
This site has everything from lesson plans to current issues in education. This site is a very useful site for teachers because it has a lot of information about issues in school reform and current issues that effect teachers.
PBS Teacher Source- http://www.pbs.org/teachersource
A great site!! This site has all different articles on current issues in education. You can also order tapes of programs that appeared on PBS to show to your students.
Teacher's Net- http://www.teachers.net
This site has information on creating lesson plans, articles, chat rooms, live discussions, web tools and current issues in schools. Live chats and bulletin boards allow teachers from all over to get ideas from one another. There is also a library where teachers can search different topics.