the admission test for St Anthony is the standard test for most Catholic schools (Kellenberg, st. John the Baptist, Holy Trinity, St Mary etc…) The admission test for Chaminade is a lot harder and to be considered to play a sport the G.P.A. thresh hold is higher. I have girls, and neither go to either school, but I do know people that attended both, and parents that have kids in both, and academically Chaminade is, without a question one of the best schools around, St. Anthony is a sports first school, it's not a knock at you, and no one said that the kids at st. Ants aren't great students, just that the admission policy to Chaminade is a lot stricter.
It's the same test regardless of the school. As for admission to one over another, it's a bit of a black box. When taking the test the student ranks the schools based on preference. So, assuming a good result on the test, where a student ranks a school may be a factor in acceptance, particularly as it relates to quotas, etc.