Twallan already made a package to deal with careers and school for Sims 3. It's called
The Careers Mod. There are three files included with that package to download and install for Sims 3. There is also a readme file that you should download and read for more details.
Part of that mod deals with school. Children can register at the City Hall to stay at home and download homework from the computer to do. Teens can choose to stay home and download homework from the computer or sign up at a vocational school (attached to different job places) to train in the fields they want to pursue, i.e. A teen wants to pursue a career as a Thief and signs up at the warehouse where Thieves work to start their vocational training. They also can choose part-time jobs in those fields too.
If there is something you want him to do for you, ask nicely.
The site Twallan is at now does not require registration to download the mods for Sims 3.