You would think that there is serious grade inflation in private schools but it isn’t always true.
My kid went to a Top 200 private school. From Preschool to 12th grade.
He is now at a Top 30 college.
It is mainly public high schools that are doing the grade inflation. And where they do it is with AP and Honors classes. All those classes, at most schools, give kids a 5.0 out of 4.0 for an A.
Take a few of them and you get a 4.2 GPA.
At my son’s school, AP courses were like a tough college level. You could barely do a couple due to the homework load.
But we know public school kids who couldn’t hang in at son’s school that were taking 5 AP courses, doing sports, and working at Walmart or fast food jobs, yet still got straight A’s in their APs.
They could make it to a medium local college but weren’t accepted to upper public colleges because the colleges knew that a 5.0 public gpa was inflated much more than a 3.6 at a Day School.
I went to a top 30 university. It was extremely intense and competitive. Most people studied like 7 hours a day. Overly competitive and not a great atmosphere.
I tutor math, and honors math at decent private schools is extremely difficult. Generally, the regular class or easier honors class is much harder than the honors classes at public schools in fancy neighborhoods. Honors geometry at top 100 prep schools usually involves 14 step proofs in 3D, and I cannot tutor that. The easier classes at private schools that are not the really top ones are not like that. There are lots of kids from wealthy and/or classy parents who are not that bright.
There are also more and more public schools you have to take an exam to get into. These are mostly similar to private schools, but like regular public schools in some ways with bigger classes, ordinary facilities, some bad teachers etc.
There are ordinary private schools and most Catholic schools, which are not that different from public schools, but usually the honors classes are significantly tougher.