Does this make sense?

[Anonymous]

At the private schools with which i’m familiar, no one gets a 4.0. Most use a 60–100 grading scale on which 90 is an A-.

Grades at the private schools follow a normal (~Gaussian) distribution such that the top student is usually around 95 or 96. About 20% of students have averages 90 or above. Another 25% lie between 85–90. About half are below 82–83.

About half of the students averaging above 90 earn admission to the Ivy League. The remaining half of these students enrol at USNews&WR top 15’s.

Students in the second tier (85–90) send a quarter to a third to the Ivies.

A means to compare a 4.0 at a public school to high grades at a private school is to compare their respective college admissions. I use an index derived from USNews&WR rankings. I count the number of grads who enrol at the USNews&WR top 15 universities and top 15 Liberal Arts colleges. At my children's private school, this was consistently a third of the class. At some more selective private schools, this index is well over 50%.

[Anonymous]

Sounds like you are trying to create a standardized GPA conversion for public/private schools and use it to predict college admissions, yet you point out diverse outcomes even within the category of private schools.

[Anonymous]

Yes, makes sense to me. Admissions staff know the school, the grading, and the quality of the students and account for it. SOP