Ultimately they WOULD catch on, and they then will want to find how it happened and take it off all of the computers. Add cost of investigation, and cost of removing software the could be a LOT more then mining profit's from CPU mining.
I suggest looking into club route still. You might be able to be adviser and get student's involved. School support would go a long ways.
It's interesting when people claim that they never promised not to do a specific thing. And then you show them the Terms of use they agreed to, complete with their signature, they become silent.