My son transferred from an out of state public high school to a New England boarding school this fall. He almost had a 4.0 at the public school and his grades have dropped (but are still high) a bit at the prep school. It’s just different at private/prep schools and most kids will have an adjustment period at the new school, just like they will when they enter college. There is no doubt that private/prep school curriculum is different from public schools and will take some time for students to adjust.