Ooh, you sound just like ds2's teacher last year. Delightful.
In school, he shows nothing, but the second he's home he explodes.
But he's "fine" at school.
So fine that last week he needed to be dragged into school by two teachers (”We just can't understand it, he's fine"
)
So fine that he has meltdowns at home in direct reaction to something that happened at school.
So fine that Dh and I are borrowing in the region of £2000 to go private to find out what's going on so we can truly advocate for him in school. This will be the first time we are putting ourselves into debt, which we can ill afford.
This is obviously just a phase. A phase that's lasted over three years now and is either getting worse or simply more noticeable as he gets older, oh, but wait, we haven't had the opportunity to label him yet 
I hope you take something from this thread op.
Too many teachers disregard what parents say, which is arrogant at best, downright offensive and disrespectful at worst. Who knows the child best after all?
Ds was observed by an ASD expert not long ago. She briefed me about what she was looking for - visible signs of anxiety, obvious obsessions, no eye contact, hand flapping, read out a long list of signs that all children with ASD show all the time. And that's why parents like me go private to get our diagnoses for ridiculous syndromes.
Learn from this, become a better, supportive teacher, who knows, you might just make some families lives better on the way.