And if you want him to stay in high school for four years, you could see if the school would allow him to grade skip to tenth, and then be retained in the tenth grade. (Weird, I know...but my parents kept one of us in the fourth grade for a couple of years, doing work way above nominal grade level, in order to stay with an exceptional teacher.) Promotion and retention decisions are generally building-based.

...pronounced like the long vowel and first letter of the alphabet...