In State Tuition for Veterans

I am at the beginning stages of understanding the Post 9/11 GI benefit and Yellow Ribbon program. My son will be leaving the Air Force in 2021. He is under the impression that he can go to any state school in the country and receive in-state tuition. My research is making me think the in-state tuition benefit is up to each individual school (potentially part of the Yellow Ribbon program?). Can anyone help clarify.

Also, how does a veteran determine state of residency? He will have been stationed at one US military base (state-side) for the bulk of his military term. Is that his state of residence? Or his permanent (parent’s) residence?

Thank you.

I think I just found info to answer my own question in the post on this forum featuring 3 FAQ. Sounds like the Veterans Choice Act of 2014 makes in-state tuition at any state college a possibility for veterans within 3 years of discharge, irregardless of their official state of residency. Or am I missing something?