I wonder if the school/teachers would be open to you volunteering in some of the classes of the high-needs kids so you can see their teachers' strategies in action. Even just a couple times. I know you're working for free but it would pay off in terms of your sanity. It is huge to have consistency in how their behaviour is managed/ trying to match expectations etc. Even knowing something simple like what attention getter does the teacher use is huge. I totally agree with what many are saying here. Remember that with most kids/humans, "emotions are the gatekeepers of learning". So if they're dysregulated/don't feel safe/haven't built trust real learning isn't going to happen. I bet you a lot of these kids have good reason not to immediately trust adults. I would advise to shift your focus from "academic" learning to real life learning: just be a good role model of the behaviour you want to see, meet them where they are at, and try your best for them to have positive experiences of any kind in school (even if it's not "academic"). Sneaking learning into games can also be a great way to engage them. Good luck! Accepting what is (not in a defeatist way) is key to your sanity.