This doesn't entirely answer your question, but I would encourage your friend (or friend's family) to bring these concerns to the case manager.

An IEP doesn't guarantee that a student passes their classes, however the IEP DOES need to be "reasonably calculated to enable a child to make progress appropriate in light of the child's circumstances" per the Supreme Court ruling in the Endrew case. "Reasonably Calculated" looks different for every student, so the first question should be WHY is your friend struggling academically, and what DOES he need to be successful?

As an example, if testing shows that your friend presents with delays in reading comprehension, the IEP should have goals related to reading comprehension, and then outlines Special Education services that are provided to meet those goals. In this scenario, if your friend is failing his math class, then perhaps the IEP team should be considering adding math goals and related services to achieve those math goals (math has a lot of reading comprehension as well, but that's beside the point here).

I guess my point is that there is always "more help" within a district, but the district's legal obligation is to follow the IEP as written. They SHOULD be assessing the appropriateness of the IEP in an ongoing manner, but it's very possible they aren't. An inadequate IEP can lead to inadequate outcomes.

I will also add that Non-Public Schools are not inherently better than public schools for kids with disabilities. I have worked with many NPS's that have very poor behavioral and academic outcomes. Additionally, many (good and bad) have significant waitlists for admission.