Most players are able to think abstractly and are thus able to understand some team concepts that are foundational to the game. They are beginning to be able to address hypothetical situations, and to solve problems systematically. They are spending more time with friends and less time with their parents. They are susceptible to conformity to peer pressure. They are developing a conscience, morality and scale of values.
Players tend to be highly self-critical.
Instruction needs to be enabling. Show them what can be done instead of telling them what not to do. Although they are more serious with their play, they are still mainly involved because it is fun. They are openly competitive. A few may foul on purpose.