Middle-grade math teachers should visit MathMovesU because it has a lot of valuable tools for classroom use.
The coolest thing on MathMovesU is a set of games for students to both enjoy and practice math skills. They set it up so that you can play the game without registering, or you can register your class to use the games and quizzes for assessment grades.
As students play, they get to explore themed settings with quizzes and games related to each location. Themes range from travel to fashion to sports.
My favorite game here is the baseball game, which lets students practice their swing, and then answer questions about ratios, percents and proportion. They can compare win/loss records and batting averages for their answers.
Another impressive game, The Sum of All Thrills, allows students to build their own thrill ride.
The website also includes an abundance of free, printable math worksheets from dozen of topics like algebra, ratios, fractions, geometry, etc. The activities also include answer keys.