Jerry DelColliano's email for Friday spends some time discusing this, regarding the blatant misuse of interns by Cumulus, a company that has no presence in STL.
Internships are granted/allowed by the educational institution from which the student is provided. My experience has been that any such partnership between the station and the student is preceded by a written agreement between the station and the school that clearly outlines the course of study and work and that a course grade must be given for the intern's work at the station.
I have also always insisted that any scholastic interns be paid at least the prevailing hourly minimum wage for the work they perform, regardless of whether or not they're "paid with a grade."
If your radio or television station is using interns in any manner other than this, you're probably in trouble.