I went my entire way through school until had a mental breakdown and was hospitalised.
Still wasn’t diagnosed by professionals until I was 37. To others I was just highly intelligent above my peers, introverted, depressed and socially a bit behind. Including psychiatrist and psychologists who saw me in hospital.
None of them flagged autism because of the ignorance of the medical profession around female presentation.
Thankfully understanding has moved on quite a bit but as many girls mask better than boys - no you wouldn’t know necessarily how much it affects them at all - even though you see them every day.
Had I known then would it have changed anything ? Well probably yes as I wouldn’t have put so much pressure on myself to be “like everyone else” as I never will be as my brain is wired differently. I never could be - no more than I could grow a third leg.
It may well have helped my self esteem. But we will never know.
So no I wouldn’t expect just a teacher to “know” or understand if a child is autistic as the medical world is still catching up let alone any other profession. But if you do want to understand I’m sure you could do a bit of reading about it. There are plenty of books and TV documentaries written/made very recently that look at the rise in diagnosis and why.
Any reason you’ve not done that ?