SimTown Elementary is a school for Preteen Sims to go to at any time of the day. It is unlocked once the Preparing For Preteens quest has been completed.
GeneralPreteens can only earn pocket money (Simoleons) by going to school. Their leveling system works with grades. Students attend school for 7 hours for levels 1-6 and 5 hours for levels 7 and 8.
Building SimTown Elementary also unlocks the Teacher career for adults. If you're Level 1-3 on Teacher, then you teach for 7 hours. But if your Sim is level 4 or 5, then you teach for 5 hours.