Dear Mrs/Mr. (insert name),
How are you today?
I am so honored that you have my best interests at heart and that you chose to recommend this wonderful boarding school for me, however I prefer the school I am currently going to as of right now and here's why.
First off, the teachers here are really great, and I feel like I am in a safe environment. I can ask my teachers for help on concepts i don't quite understand and expect great answers. In, addition, this school is close to home, which means that, god forbid, something happened to me or a close relative, I can be picked up within moments notice. My parents wouldn't have to go through so much trouble to get me out of school, for the simpler matters either, like a doctor's appointment. And lastly, I can go to school with people that I know and am comfortable with. Changing schools halfway through high school can be tough for kids my age, who have grown up with the same people around them.
So I hope I have convinced you of the benefits of going to the school I already go to and I hope you understand that I am very grateful to have a person like you who has my best interests at heart.
Sincerely,
insert name