I feel for you in this - its tough being someone who just gets things, as you spend all your time treading water and trying to keep yourself motivated when others are automatically motivated because the pace of the lessons is right for them. That said, its really important to get him to understand that learning how to work when you don't know something is really important - one horrible risk when you are really bright is that you have never had to learn how to work and give up if you don't automatically understand things - It may be that he actually doesn't know what to do - how to decide what he does and doesn't know, what strategies there are to get you to remember and understand things that are not automatically understandable etc etc.
I know this feeling, I didn't work at o-level - did quite well, I thought 'oh my god I will have to learn how to work at A-level' but didn't.. and got 2A and 1C. I thought 'ohmy god I will have to learn how to really study' at University, but didn't and got a 2ii. It was only when I realised that I could have got a whole load more out of Uni if I had learnt how to work, and also when I wanted to learn a whole load of employment law, HR practice, and Industrial relations information to go for a job ahead of a rival, that I really got my arse in geear and used strategies from project management work in learning. It was the first time I'de really worked academically in my life and I did MBA level learning and finished a law revision self-assessment book after four weeks. I am 38 and far too old to be learning this, but this may happen to your son if no-oine is careful.
I also remember thinking (in a rather 'Sandhurst' way) that anyone who did extra work was cheating because their exam results wouldn't measure how clever they are, just how much they can work - that belief didn't leave me even at uni.
You need to get him to learn something inside out that he is really enthusistic about and try to transfer the learning about learning skill to him. Its difficult if, as you say he comes across as lazy because teachers will misread this as an attitude problem rather than as a symptom of a legitimate response - ie. if I really work hard everyone hates me, I get frustrated, I don't get better grades and I have to repeadedly think about things I already understand whilst others aree catching up - i.e. is less psychologically traumatic to switch off and wait (Hare and tortoise).
You could try some philosophy, some discussion about hs work strategies and then debate that nice anaolgy, but it might be just as good to point out that someone doing well at uni can earn £36,000 four years later(see Maths and Operational research graduates!) and be one of the richest 10% in the county five years after A-levels.
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