Hi OP, have been through this with a younger teen. PPs are right: so much of this is now working with school to reduce environmental stressors, and ensuring adults in his life are behaving with understanding and compassion.
The tricky thing with an adolescent diagnosis, is that it can profoundly disrupt a young person's sense of self, at a time when social identity is pretty fraught for most young people. And let's be truthful, whilst the narrative of neurodiverse difference is now used in many institutions, their actual practice is often still deficit-based. The process of securing support can feel very negative to young people, who need to be included given their developing capacity for decision-making, but who find it predictably humiliating and undermining to have to keep on documenting all the things they struggle with. I don't know what the answer is, but I wish services were more careful with our kids' self-esteem and confidence.
The general challenge is obviously that everyone's autism is unique to them, and if you need to support your son by advocating for him at school, you need to quickly develop a sufficiently nuanced understanding of his autism, and link this to concrete ideas as to how any related needs could be supported, in a way which HE feels would be of positive benefit. Depressingly many schools/LAs will do/suggest very little, so please don't underestimate the challenge or lead time to getting even small adjustments or provisions actually put in place.
The things that have really helped us with this have been to read a lot, especially autistic people's writing about autism, and whilst expensive, to get a detailed assessment undertaken very sensitively by an independent EP, which DC was able to comfortably engage with, and which has unlocked a very much more detailed understanding of DC.
If you want to take a deeper dive into neurodiversity there are a couple of decent free MOOCs you might want to look at - a really really excellent one on ADHD (including latest evidence/debates on medication) produced by King's College and one on Autism produced by the Univ of Derby. Loads of charities and CCGs have produced online resources for families and young people, but finding teen-appropriate content takes quite a lot of filtering.