Grade Inflation and Vice Versa

I’ve noticed that there are a couple of applicants (perhaps including myself) who have SSAT scores and grade that don’t exactly match up. For example, there might be an applicant who has straight A’s but repeatedly scores below average on the SSAT, and on the flip side an applicant with scores in the 90’s and a 3.4 GPA. I understand that neither of those things are particularly helpful when applying to prep schools, but I was curious as to whether or not else here had an opinion about the impact of these two things on admission. That is, ignoring outliers such as international students with good TOEFL scores, students who had medical emergencies and couldn’t attend their classes, etc. . Thanks in advance!