IMO if by sixteen you haven't applied yourself to learning maths then you are probably unsuited to an occupation requiring any application of maths. You probably need to look for further training in a more physically based trade. Those that are coping well with maths will probably have the sense to choose it as an option going forward anyway, so need no compulsion. But those having difficulty are the only ones likely to benefit from a compulsory continuation, but not for anything new, but a last chance to get the basics straight before they find themselves out in the real world, not best equipped to handle it.