Here is another site dedicated to understanding and solving math problems. What's interesting about this site is that English and Science are incorporated as well. It's a known fact that these 3 subjects are dependent upon one another and understanding these subjects (as a whole) is essential. This site is geared for the primary grades.

This is an interactive site for elementary and middle school kiddos. The games are quite engaging and make learning math a lot of fun.

what's really 'cool' about this site is the use of word problems which are often difficult for someto grasp the understanding of completing such a problem.

Although not a free site, Zoodles has a great deal of interactive games for the various primary school age subjects. My 10-year-old enjoyed the free trial so we're considering purchasing a membership for 1 year. Subjects include reading, math, science, and writing.

This is the main site where I pulled the crossword puzzle game from, it has games for K-6 students.

This an interactive crossword puzzle about outer space, specifically stars and planets.