Dressing for an interview?

I have an interview this weekend for this network of schools that I applied to, and I really want to make a good impression. I recently got an e-mail telling me that dress for the interview is comfortable/casual, but how comfortable exactly? I mean, jeans still seem too casual. At the same time, we're doing group activities so that the interviewers can ess our ability to work as a team, and I don't know exactly what the activities are. If they're active then I don't want to wear heels that are going to be a hindrance. Any suggestions?