"Been done before and maitanence bills went through the roof"
Maybe the school should have done a better job teaching them?
"The school will factor in the fuel costs"
So now, in addition to not being taught correctly, they're paying more for their flying than they ought to?
Leaning the engine is an important part of flying and engine management. So instead of treating students like they're idiots perhaps they should be educated? This may then reduce the amount of half-truths and rumours which only serve to make the situation worse.
Jeremy Pratt has a fairly extensive section on this in one of his books. So he seems to think it's worth teaching.