I'm really sick of people saying that you shouldn't wear a suit to a career fair. I understand the implication those who say it are trying to make, but it just doesn't work out that way. Any career fair I have been to, especially when it's for students, the kids dressed down are not doing so because they are confident and talented enough to not worry about impressions. Instead, those are the kids who either did not care enough to prepare for it, possibly have a class assignment that requires going or most often, just take themselves too seriously to be a viable candidate.

Also, to recommend that someone dresses down for the few positions that might be okay with that really limits who the student can meet with. While a few companies may be casual and willing to take someone in who didn't put the time into even preparing themselves for the career fair, many companies (including quite a few bigger companies that would be more likely to hire and invest in new talent) would be turned off immediately.