The new Common Core standards emphasize skill mastery in Math. These two activities can be used to promote mastery in nearly any grade level and with any Math skill.
The first, Go to the Head of the Class, is based on the board game of the same name. Students physically move in the classroom based on their master level. The second, Error Analysis Boxes, students get instant feedback about their common errors.
You can use these activities over and over again. Students love them because they produce results! Teacher loves them because they leave no child behind!