Something that I think people realise very late is that drive, ambition and levels of basic laziness ARE a key part of 'academic potential'.
It's not necessarily the cleverest academics who get to the top, or those that have the best/most original ideas... it's those who will doggedly put in the hours writing papers etc., those who will slog at it.
You can probably transfer this to pretty much every industry I imagine.
You absolutely cannot influence it at this stage, but what might happen is that when he fails at something (could well be his A-levels) he will realise that he DOES have some of that drive, and will start turning that element of himself around.
In that sense, it's far better to mess up A-levels than swing those but mess up Uni/placement/first job/whatever.
But however you look at it - in terms of achieving 'success', your ability to put in effort, concentrate, work, not be lazy - they are part of your academic ability, not something that just 'affects' it.