My son just turned 8, and was supposed to start 2nd grade in the states, but due to circumstances he's started school here in the UK. I had a talk with his teacher, and it seems to me the schools out here are a bit ahead of the schools in California. However, she assured me that he won't in any way be behind or held back for his time here. Now, that's only for this year, I'm not sure how a prolong period of time would effect him. Might be worth having the same conversation with his teachers. Good luck- hope things work out for you.