I teach jr/sr high, so students who are not adults. The ability for the instructor to age-lock the student accounts in some way would be good. This could be difficult if the accounts are non-expiring or if, at the end of the term/year accounts can be rolled over into regular accounts. ("Ms. Teacher, my son used the account you gave him to read porn!") (It might be better to actually make this a university deal at first *ponders*)

Some kind of export function, preferably to PDF, for posts and comments, preferably selectable by tags (so for example, you could print to PDF all posts tagged "Creative Writing Project", but not "brainstorming" or "teacher announcements"). This would be great for making class books, and for keeping feedback.