Yeah, I let that site die and now I think there are some better ways to do what I did then.
Still, I think that having sets of topics with whatever you call “assignments” in a read only category so that people create a topic with their “answer” on some category with a tag indicating the assignment is workable, perhaps with a theme to smooth the ux.
There are also some tricks to create links to start a new topic that could help, for example.