9 year old slow to develop - should we push him?

[Snowybird]

My 9 year old DS has developed very slowly - school says he is very, very young for his age. He has a twin brother who appears to be about two years older in his general maturity and attitude. DS is getting good scores at school so the teachers don't see a problem. However his ability to focus on anything and commit to it is very noticeable and becoming a problem. He loves playing the clarinet and has played for nearly three years now. But although he aspires to taking a music exam he just won't commit to any sort of practice, just seems incapable of doing so, rather than just lazy. School says that this is normal in an immature 9 year old and we should just give him time. On the other hand he does need to learn self-discipline sooner or later....preferably before school work starts getting more difficult.
What would you do? Cajole him every day until he learns self-discipline, or let it go? (we already did this last year)

[SaffronCake]

I would let it go. You can't make him into someone else. You run the risk if you push him of him resenting you, seeing his brother as his rival, feeling suffocated and of him being deliberately lazy and starting to underachieve to spite you. You have a healthy bright boy, the boy you and his Daddy created, love him for his positive qualities.