One of those apps I enjoy sharing with teachers is Math vs Zombies. The name alone will get the boys in your class excited. The object of the game is to turn zombies back into humans by correctly solving the math problem above their head. Even though the app is $4.99, it is worth checking out and using with your students.
Students can select from the four operations (addition, subtraction, multiplication, and division). There are also multiple levels within each operation.
One recent addition to this app was the ability to access reports that are correlated to the CCSS. You can view reports from a grade level stand point or a operation stand point.
The only downside to this app is students can not have their own account, so the reports will be cumulative. The app has a whole though is a great addition to a math center rotation in multiple grade levels.