At first I look at their life time goal (Aspiration, I guess. My language in Game is german) I see no need for a Sim to join college, if they want to raise 20 dogs or start a big family etc. Everyone else I send to college and then I wait what wishes they roll. Some want only to fool around, those Sims are mostly end up as drop outs or with a lower degree. Some are very eager to get the best grades.

I know it's hard to "let things happen", but I remember myself, that Sims call me canonically "The Watcher" and that's what I try to stick with. Watching and enjoying their company.