If you are teaching math, you might want to encourage your students to try out this site for math games: https://tangmath.com/games

These games are not Flash based, so no frustration when they don’t work like you can experience on other sites. They also are really about MATH and not just hopping and shooting like other, less academic “math” sites. This site also sells Greg Tang’s products and training opportunities, but most of the games are free to play.