I went to a private school with a sprinkling of PGs. A few were were future West Pointers looking to keep playing D1 Hockey, they had some sort of academic shortcoming that had to be rectified.. We had one PG from Canada who had played junior hockey and was trying to get a scholarship.
In most cases they were targeting private northeast schools with academic standards. Some were just hoping to get a few more options. We had resources to help people with SAT test prep, and some probably had learning disabilities so there were resources for that. It was really just a repeat of their senior years. I can't think of a single case where the student and the school didn't benefit.