If the school is against acceleration, would they consider single (or multi subject acceleration)? What other options would they be willing to provide?
We have our PG child in a parochial school, which has supported subject acceleration (two years in his case, could work at a higher level, but the fit from a workload standpoint has been appropriate so far, i.e. not doing high school hours of homework).
There are families who have successfully managed public school with PG children. So much depends on school flexibility/mindset and the individual child. For example, our school has been flexible, but DS has not wanted to completely leave his age peers. The combination, along with weekend gifted programs, unlimited library access, etc. is working well. For now.
