That's definitely tricky. I didn't get an opportunity to accelerate until I was in middle school (more than a decade ago, granted), but, once I had done it, I found that the older students in high school, especially some of the juniors and seniors in my classes, were a lot more accepting of me than the students closer to my age. However, I had been friends with some of the older students before I transferred into their classes and had no friends in my current grade. Does he have any older friends in the classes he would be taking at either school?