So If I repeat 9th grade next year, do my grades still count or affect my college application?
The 9th grades from your prev school probably wouldn’t count.
I think you would be wise to investigate the school you are applying to. For example, Choate will offer you Q credits for your past core courses or summer courses. It may also be possible be bumped to honor level. Check with your school.
Slightly off topic: will my GPA at BS take into account my freshman grades from my current school? (I’m not repeating.) @HistoryGeek40
Depends on the school, but usually not. Additionally, some BS’s (certainly the case with mine) do not provide a cumulative GPA.
When you apply for college you will need to submit the grades of the repeated year as well. The grades DO NOT get lost. (I wish that was the case) This applies to all private boarding schools.
For most schools-- won’t count in GPA at your BS, but will get reported to colleges.
Colleges seem to ask for all grades earned in high school. In other words, repeating a grade will not hide a bad 9th grade year.
On the other hand, there is the opportunity to explain how you have overcome challenges and difficulties by changing schools.