The previous couple of posts bring up the issue of clear standards - or lack thereof. If any interference with the controls or anything else happened because the student didn't meet the standards (i.e. acted downright unsafe or potentially unsafe), that should have never been kept quiet about by the instructor. That's what an instructor is for - ensuring that the process of training is not just some formality but a path towards achieving consistently safe performance well within any existing margins and tolerances. If the student is underachieving somewhere, that's never best dealt with by quietly fighting him on the controls and not giving any feedback and guidelines for rectification of the problem.
If anyone has the mindset of "OK, I'll just push this guy through until he's not my problem any longer", they simply shouldn't be instructing. Teaching is one of the greatest responsibilities you can take towards an individual and the society in general - and you shouldn't do it unless you feel a moral responsibility for the end result. Especially whenever an unsatisfactory end result may lead to loss of life.