Perhaps this will help. After having one too many expensive bikes disappear to never be seen again and not really liking beaters i decided to by a folder (Brompton). Never to leave a bike outside again. Had a few other cheaper brands first but all too big a fold and/ or crappy bikes. The Brompton was picked for a number of reasons. Small fold which meant not likely to be hassled taking it inside anywhere. Lack of room at my abode. My motorized vehicles are getting smaller the higher gasoline goes in price. I like to throw it in the trunk when i go visit friends in other cities so i can ride around there towns to see the sites. I have never been hassled bringing it in even libraries, museums etc. The one time i was, i just asked if i put it in a bag would it be alright. The answer was yes so out came a large garbage bag and in i went.
If you are going to leave it outside buy something cheaper like a low end Dahon used or new, or the equivalent. Dont buy whats considered higher end folders like Bromptons or Bike Fridays etc. Better to lose couple hundred bucks and attract far less bad guy attention than expensive bikes. People are starting to know folders over here in North America and many for sure know the higher end ones.
People put Bromptons in those bags you can get for $2-3 bucks at Ikea stores,surely you will be allowed that in a class room. Im sure some students carry that size stuff with books etc. in them.
Guess im reiterating what nearly all the others here have said. Your asking alot of folks here with lotsa experience. Hope it works out for you.