summer2468:
The language the Wharton AdCom is using is very similar to that which many of the schools use in describing their letter of recommendation requirements. The strong preference is always for supervisors or bosses to the extent that is permissible.
If you have limited to no work experience (because you are still in school) and getting a solid recommendation letter from a work person would be challenging, you can almost surely get one from a college professor/teacher. You can make the argument that school is your "work" setting and your professor/teacher is effectively your supervisor. You may need to explain in the available optional essay why you felt these recommenders were most appropriate.
If you are still uneasy about the language in this requirement, I would call up the Wharton MBA Admissions Office and see what they say. There's nothing like hearing it directly from the horse's mouth!
Good luck,
Admissionado