I may have missed something, in which case I apologize... but instead of re-reading I'll use the limited time I have available at the moment to mention that if your son truly wants to achieve agreed-upon goals but seems unable to, is it possible that he may have a difficulty with Executive Function or other 2e issues? Might he be leveraging his high intelligence and social nature to compensate?

Just in case this may be a factor, here is a brief roundup of links on Executive function:
- partial list of EF skills issues
- resources to help a child understand ADHD
- Understood.org - executive function skills
- Wrightslaw - executive function skills
- books to help with EF skills: Smart but Scattered... Late, Lost, and Unprepared (hat tip to aeh)