Chess.com: http://www.chess.com/
Chess for Kids: http://library.thinkquest.org/6290/
Chess Kids Academy: http://www.chesskids.com/
Free Internet Chess Server: http://www.freechess.org/
Mark Lowery's Exciting World of Chess: http://www.markalowery.net/Chess/index1.html
Wikipedia: http://en.wikipedia.org/wiki/Chess
Neither I nor CES/MCPS is responsible for the content of the above links. When I visited these links, they all appeared to have appropriate content for students of upper elementary age, but they are subject to change at any time without my knowledge. Some of the links above include ways for students to play in chess games or visit forums where they may have contact with people outside of school. It is always important for supervising adults including parents, guardians, and teachers to monitor children at all times when they are on-line.