FFB, I think your specific problem lies with the fact that there is not only is a lack of standardisation in training organisations, there is also a lack of standardisation amongst the students! Sounds like you are trying to teach a smart@rse.
They pop up occaisionally, even in heavily standardised organisations like the RAF. Letting him make mistakes after he's told you what others have tought him is the best policy IMHO. After a while, his slow progress will hurt his wallet and he may decide to follow your advice.
There is of course the danger that he may give up. Some may throw up their hands in horror at this notion, but in my experience this level of 'smart@rsedness' goes hand in hand with overconfidence. I had experience of once chap like this. We persevered with him and got him through his training, and eventually he joined out aircraft syndicate - despite my protestations. He subsequently proved me correct by crashing our aeroplane!