It begins with a review of the planets in our solar system. Then it continues on to cover info about each of the planets. This site is good for review or introduction. However it is not necessarily a game site. This site is not interactive, but it is necessary for 5th grade curriculum.
Subjects range from math to literature to sports.
At this site students can construct things out of masses, springs, and muscles. Science for middle school and high school but could be used for 5th grade. You must use your skill as an asteroid hunter to neutralize the asteroids in each sector. For grades 4 and up. This site has many examples of visual optical illustions.