The preteen life stage is only available in The Sims FreePlay. It is similar to the Child stage in other games.
Preteens have several hobbies which earn various prizes.
The amount of money (allowance) and XP your Preteen will earn from going to school depends on their grades. The higher their grade, the more Simoleons and XP they will come home with.
A Preteen can improve his or her grades by going to school every day, as well as studying with a Study Desk when they are at home. You can purchase a Study Desk from the Home Store, under the 'PreTeens' tab, for Simoleons or Lifestyle Points.