Free Teacher accounts can be created at SumDog a great site for math games designed to improve numeracy. Once your account is set up you can then create accounts for your students with avatars, logins and passwords. This enables you and your students to view the progress they have made over time. In addition, students can play against (or with) each other.
Without an account students still have access to the games they just can’t create their own avatar or play against classmates. Either way students will enjoy the games at Sum Dog.