What a dilemma.
Your sons levels of frustration appear to be an issue, which reflects in his behaviour. His social communication skills, affected by his apparent difficulties to communicate his needs, difficulty articulating what he wants to say or what he has heard. Has he been tested for Auditory Processing Disorder? This means that hearing is fine but brain has difficulty processing what has been heard, thus responses could be in inappropriate or misinterpreted. The approach is speech and language therapy. Auditory Processing Disorder can run parallel to A.D.H.D. as can other conditions.
The schools response is a double edged sword. Keeping him back a year to improve his social skills whilst his peers move up a year. The school is basically saying that by being in a year group that is in your sons chronological age they hope that this will improve his social skills, whilst acknowledging that he is above average academically. It is an unusual approach.
your sons emotional well being should be one of the major considerations. It would appear that your son knows he is different and the lack of friendships could be impacting on his sense of self worth. His adverse behaviour apart from poor social skills is also a form of attention seeking. The attitude being if I play up people/peers take notice of me. To onlookers who don’t understand the child’s difficulties consider that your child is being very immature.
Mum try not to let your anxieties transfer to your son. I know easier said than done.
With your son being “Bright” it is important to be aware that we don’t kill his motivation to succeed academically.
I have known some kids who choose to underachieve in order to “fit In.”
Your son could benefit from seeing a therapist to improve his social skills/social interaction skills and social imagination skills. Perhaps he/she could start with some play therapy or art therapy. If you do decide to go down this route hopefully the therapist will give you some coping strategies.
You can contact me should you want a few ideas.
good luck to you and your family.