My non CAH husband was excactly like that as a child as well.  He is very bright but never applied himself at school, only doing what was needed to get by.  He got a university degree but probably not in his chosen field and he now regrets that he didn’t work harder.   We now have a 5 year old CAH girl and she is also very bright, however she hates failure and will often not even try something because she "won’t be good at it".   I have a feeling she too will not apply herself at school to her full potential and will only do what she has to do to get by.    She works best when there is something in it for her at the end, i.e. a reward.  Maybe you could set realistic goals for your son and offer rewards for getting the result.  Maybe for getting a higher grade on his report card than the last one you could take him somewhere special, or for achieving something in the classroom that he has been underachievning in.  You may need to liaise with the teacher to discuss the areas for improvement.  Most kids seem to respond really well to rewards.  Best of luck, I know how frustrating it is to see your children underachieving.