What about a move to a different school, but still at the age appropriate grade? We changed DS (socially delayed too) from a "high" performing public school (meaning best rated for the immediate area and with some bright kids) in a rural and overall low or mixed socioeconomic area, to a extremely highly rated school in a high socioeconomic area, still within a possible driving distance to jobs, and there is really a shocking difference. It's wholly a different experience, and both public schools within the same state, and I think well worth the lifestyle cut for us. A reasonably happy DS is a huge weight off our shoulders.
My take on it is first you find a school that really will work with you and looks good overall, who seems very interested in your individual child, where the teachers all seem nice and accommodating, and then only second decide if a skip is needed in that particular school. If it is a private school then it needs to pass a higher bar I think ahead of time, because their incentive is to sign you up and not necessarily to provide years of minute to minute accommodations.
So how is this school other than the offer of a skip? How is your current one? Can you observe in the classrooms of both of the possible grades in the new school? What do you see kids doing? Do they talk to the adults or are they silent? Do they speak to eachother during class? Do they look happy when they are done a worksheet or what do they do then? What do the teachers/principal suggest about helping him socially? Do they mention other kids with similar issues of both Es? When you observe do you see kids doing widely disparate things in the classroom, is there going to be differentiation beyond a skip (because a skip likely only helps for a year, maybe two or three, the pace is usually the problem). When you observe are the rest of the kids bright seeming? Is there a great teacher student ratio? Etc.
