Confusing Words is a handy little website for any student writer. Confusing Words is an index of 3210 words that are commonly confused or misused. If you’re not sure if you should use the word “affect” or “effect” type either word into the Confusing Words search box and find your answer.

Applications for Education
Confusing Words could be a good reference tool for student writers. If you maintain a blog or wiki for your class, Confusing Words may be a resource worth linking to.

Here are a couple of related resources that may be of interest to you:
Writing Fix
Grammar Bytes