I attended the American School in London in the 70's/80's and found that this eased the lifestyle adjustment greatly considering my peers where international or North Amerian for the most part. It was expensive but worth every penny. If you're outside of London the TASIS or ACS (American Community Schools) are good options and generally less costly. Switching to a British based education will have some effect on college plans if your son is planning on returning to the US later. I personally think that 10th grade is hard enough without adjusting to a new curriculum/culture, so would do all I could to stick with the North American system.