I believe the correct answer is: a token economy.
A token economy represents a form of behavior modification which is designed to increase desirable behavior and decrease undesirable behavior with the use of tokens. When individuals display desirable behavior, they receive tokens. The collected tokens may later be exchanged for a meaningful object or privilege.
Since Tim suffers from attention deficit hyperactivity disorder (adhd), his teachers and parents apply a token economy to reward him with stars for desirable behaviors.