"High test scores often grant college credit at a public university – which means, very tangibly, needing fewer credits and tuition dollars to graduate – or a “you took a hard class” gold star (though no credit) at a private university."
Every private (US) university I applied to was willing to offer AP credit, given a high enough test score. The vast majority of my (private US high school) peers took AP exams, went to private universities, and received credit for their AP classes. One of them earned enough AP credit to enroll at Harvard as a sophomore.
I've never heard of AP exams being a "Public Universities Only" thing.
I'm currently a freshman at an Ivy League school where no credit is offered for AP exams, and I believe that this policy is similar at many of our peer institutions. The exams can be used for placement purposes; however, they aren't really that necessary considering that prerequisites are very loosely enforced. I think the most important use for AP exams is actually during admissions. An applicant with an AP class on his or her transcript but with a low or missing AP exam score may cause an admissions officer to question the rigor of the class.
We do have one program that allows students to graduate early or earn a masters degree in four years. Most people here have enough AP credit to do so, yet they rarely elect to use it.
I went to Rice which was rather generous with AP credit. I used AP classes to cover lots of my electives and some intro math and science stuff. I skipped all the calculus requirements via AP. Some classes however only allowed you to skip classes without actually any credit granted. I think this varies quite widely by private universities.
I looked over the schools I applied to (over a decade ago) and it seems like the Ivies have gotten a little pickier about giving credit for AP exams.
I just spot checked some of the brand-name non-Ivy schools that my friends attended and all but one offer actual college credit for AP exams: Stanford, Northwestern (varies by college; I only checked one), Carnegie Mellon, Georgetown, Johns Hopkins, and NYU all give college credit for AP exams. Boston College only offers advanced placement.
Every private (US) university I applied to was willing to offer AP credit, given a high enough test score. The vast majority of my (private US high school) peers took AP exams, went to private universities, and received credit for their AP classes. One of them earned enough AP credit to enroll at Harvard as a sophomore.
I've never heard of AP exams being a "Public Universities Only" thing.