In addition to what Bill wrote, please do flag questions tagged homework for closure if you think they should be closed. If they're closed, leave them alone unless you think they should be reopened. Questions with a flag for closure are shown to a queue to users with close privilege who can then cast close votes (or not, if they disagree). Be sure to use one of the predefined close reasons, not custom text; for homework questions, common close reasons are “too localized” (questions containing a big code dump where the answers won't help anyone else) or “not a real question” (when the question is just a dump of an assignment, it's usually too broad).
One important guideline when deciding whether to edit or close a homework question is whether the thread is likely to be useful to future visitors. There are two aspects to that:
- Will someone having a similar problem be able to find the thread in a search?
- Will someone who finds the thread get some benefit from the answers?
If the answer to these two questions is yes, even if it's a weak yes, please edit: at least to remove the homework tag, and if necessary (which is often the case) to improve the formatting, the title, the English, the other tags, etc. Also, if you can help the thread along by adding a worthwhile answer or by adding some search fodder, please do so. If the thread looks good, don't forget to remove the homework tag.
If the thread isn't salvageable, do leave the homework tag, and flag for closure as applicable.