Wish I had better news for you. But after fighting and fighting with a top private school for 2 years (who also gave us lip service), we decided to homeschool starting this summer. DS6 LOVES it and never wants to go back to school again. Our issue is that he likes to spend HOURS pursuing a topic - for months. The 15-20 min activity time in school drove him nuts. The schools are just not able to let a creative mind roam free and explore for hours on end.
DS is on the immature side socially. He loved school from the social aspect. But hated that he was bored outside of the 20 min recess. The school was never going to let him advance until his social caught up. It is not likely to ever catch up as it is part of his asynchrony.
If you can swing it, homeschooling is an extremely attractive option. In our area, the social events and classes tend to be more multi-age, so DS can be a younger kid in a group of older kids and is MUCH happier. We've also been successful getting him into a writing class 2 grades above his "age" grade.
Wish I could be more help. Those who fight with the school really fight. It's a lot of effort, but worth it for those who are successful. It just wasn't worth it to us.
The school's position is ridiculous, the immaturity is exacerbated by not being with more advanced peers. I am on the threshold of getting DD accelerated one grade because of this. I scoured the web for articles ( including asking others here ) for articles showing that acceleration ahead of social development was a bad thing and found *nothing*.
I then forked out for the IOWA Acceleration scale and showed the school staff - when you have IQ and achievement scores to back you up it is harder for the school to justify holding someone back. The IA scale also gives the school some CYA because it offers them a chance to a) answer any accusations of favoritism and b) provides a tool that the school can use to help other gifted kids.