What an interesting discussion!
My kids have only been in school in the UK for the end of Reception (2 months last year) and the beginning of Year 1 this year. My goal is to move back to the US by the time my kids are in high school and I wish we could go back before my step-son goes to high school (he is 10 and will be going to Secondary next year). He is very high functioning, but on the Autistic scale, and he does really well academically but is starting to get teased (I won't call it bullying really) for his academics, which I don't think he would if we were in the US as he would be in honors and AP courses.
My 6yo twins are thriving in Year 1. They are in separate classes, which really helps them, and one was elected to school council this year. They were both in the Harvest Festival play, which they loved. And they are in the Reading Recovery program since they missed almost all of Reception (basic phonics, starting to read, letter writing, etc) last year, which is a 30-minute individual lesson every day to help with their reading, phonics and so forth. They have advanced from level 2 books (below National standard) to level 8 (in National standard, but at the lower end) in less than 10 weeks with the goal to level 15 by the end of 20 weeks. They can sound out words and write and are learning basic spelling, which they refused to do (write) at the beginning of the year. I don't think they would have gotten this intensive, individual course in 1st grade in the US. Now, of course, the school is doing all they can to make sure they pass the National phonics test at the end of Year 1, so it is in their best interest as well, but I think catching and helping them early, so they don't struggle later on, is the best for my children, as well. Their teachers have both said they are just blossoming and one loves writing stories and their other subjects have gotten better with being able to express themselves better.
We are in the waiting period for being notified of Secondary schools for the older boy, so fingers crossed for us that he gets into the better school (we are in one catchment and his mom is in another, so at least we have access to two sets of schools!) but we have been waiting for the Autism Support people to come visit him for almost 2 months now, and I know getting services for him in the US would have been easier in this aspect.