Nothing! They told me in school that we can't use the student version to make money and such. I'm sure Adobes website spells it out somewhere, but as far as the program their is no difference.
Edit:
Think of it this way, Adobe wants it's program to be what professionals use. So if they allow students to learn the software at a discounted price they will turn around and use Adobe when they become professionals. They don't want students to only learn 1/2 of their software so theirs no difference between student and full versions.