We had a bit of a discussion about this, about a year ago - and the general idea I got from it wasn't that the penalties stacked (outside of the Teacher/Student one, which is RAW), but that there's a boatload of other consequences of putting a bunch of Gifted students into a room with each other, without the benefit of Parma. (Although it's pretty much all talked about on the last page of Apprentices, which is summarized on the last page of the thread).