According to the school despite working above grade level in all assessed areas they do not feel that he has fully completed the complete 1st grade curriculum and socially/emotionally it is in his best interest to attend 1st grade next year!!!!!!!!!!!
If a child has no friends but does age appropriate work, social/emotional issues never factor into acceleration. Present them a gifted child and it is primary factor they consider. Ask your school how his social and emotional wellbeing will benefit from being bored silly all day.