I can't offer much more than AEH's exceptional advice. Other than wanting to point out that not accelerating is not a neutral choice. Your child is so gifted that the teacher and principal have approached YOU, this is not a common scenario, you need only spend some time on this board to find out how often families struggle to negotiate subject or full grade acceleration which they believe their child needs. For the school to make the suggestion implies that your son is very gifted, and quite visibly different from his peers. It also suggests that he would be accelerated within a very supportive environment, because it is THEIR idea. If your child is so different that school have noticed and proposed a skip you must consider that the children will also be very aware of his difference and THAT can also lead to social problems.
When children are very different it can unfortunately cause social problems. If he is the youngest in his class, that is one way of being different, it has risks. If he is very noticeably intellectually different from his same age peers, that is another way of being different, and that also has risks.
Acceleration risks possible future problems (especially for smaller and quieter boys, as AEH has noted). Not accelerating risks more immediate social problems and long term impacts on a child's engagement with school and learning.
Personal anecdotes:
I have one child who is one year accelerated, there are problems at times. Every time teachers, or anyone else, points out a problem and blames them on the skip, I will ask "Do you think they would be better off in their correct grade". The answer to this is always somewhere between expressions of abject horror and "NO! Of course NOT!" or slow consideration followed by "No, no I really don't think so, I think that would be worse". There is no "best" solution to my child's problems. There is only the least worst thing we could do at the time, and it has continued to be the least worst thing anyone can think of.
I have another child who we did not accelerate during grade 1, when it was discussed, although they fully met the IOWA scale criteria as an good candidate. I deeply regret that now, mostly for social reasons. Despite having started school a very socially advanced child (the school also commented on this throughout the first year of school, it's not my imagination), they just didn't fit in and were bullied fairly relentlessly through gr 1-4, across two schools. They are now home-schooled, have significant social anxiety and have learned some fairly negative social strategies after so many years of social failure. This child was my "easy child" (the school also talked about this one being my "easy child" during their first year of school). Or so we all thought...
I should note that my husband is very tall and my children are all tall. The eldest happily had their growth spurt late, so wasn't the tallest until about yr9-10, despite being in the correct grade (though young for grade). The child who is 1yr accelerated actually would have stood out like a sore thumb height wise if they had not been skipped, as they were one of the tallest in their grade even with the skip. Due to their physical size one of the problems my child has had with their skip is that teachers don't remember that they are skipped, and that is good in some ways but problematic in others.
