Teen Sim Won't Attend Afterschool Classes (Sims 3 Generations)

@Derp54590  I don't think your save is broken (and definitely not that you're an idiot).  This is a known issue with field trips and afterschool activities; it doesn't always happen, but it's been reported since Generations was first released and was never patched.

There are a few different approaches here, depending on whether you use mods or are willing to try a few.  One is to install NRaas Overwatch, which I believe fixes the problem all by itself.  If it doesn't, adding NRaas MasterController and running a town reset (click on City Hall and select NRaas > MC > Town Options > Reset Everything) should also fix the issue.

If you don't want to use mods, you could evict the household in Edit Town and put them back.  They'd keep their jobs and relationships but lose their promised wishes and opportunities.  Or you could bulldoze the school and put it back.  In either case, the children's grades would reset to zero, and it's possible the progress in the afterschool activities would too, but I can't confirm because I've never tried it for this purpose.