My advice (as a BGO) is to dress as if the interview is an important part of your day, regardless of where the interview takes place.
For most folks, that means changing out of the shorts, jeans, t-shirts, gym clothes, etc. that you wore home from school into the basic equivalent (for men) of pressed pants a collared shirt and close-toed shoes with socks. You can be more dressed up if you prefer but most BGOs will be satisfied with the above.
One thing if the interview is in your home . . . I know it's customary for a lot of folks to remove their shoes upon entering the home and to ask guests to do so. However, unless there is a REALLY GOOD reason, I would not ask your BGO to do it. He/she may offer but it could be really awkward (especially for females who may be wearing dressy shoes without socks) to have to walk around in bare feet or if a sock has a hole in it . . . you get the point. One person wearing shoes for one hour won't harm your carpet, your floors, etc. (Obviously, if they have to track through mud to get to your house . . . different story). I would also suggest you wear shoes for this one occasion so as not to make the BGO uncomfortable. In any event, you the candidate should not be barefooted/no socks (as I have had happen). Just a recommendation . . .