Just because something is commonly practiced without choice, doesn't mean that it is legally defensible, which is what the person above was questioning.
Authors generally have right to their works by default, even students. Those who use copyrighted works for academic purposes do get some exceptions to copyright law.... but a commercial service is not this.
Furthermore, student assignments are additionally protected by FERPA.
I'm not sure the answer, but I do think it's a great question.
