Claw - I just wanted to add a few of things to Star's advice.
Firstly, as you know, my DS presents in a rather similar fashion to yours. He certainly presents differently in different settings. By this I mean, he would rather say nothing than scream about a problem like he would at home. It grates massively when school say things like 'we don't see that here' as if it's my fault. However, this does not mean that specialists in ASD think that. This is CLASSIC behaviour from a child at the high end of the spectrum. They 'hold it together' at school and will often only act in a 'normal' way at home or will only express their anxieties at home. School do not understand the school-home continuum and how one affects the other and that is the problem you have. It does not mean the ASD specialists won't understand this and make recommendations for a clearer/more relaxed environment for your DS at school.
Secondly, remember too that the ASD team have seen your DS and will have made their own minds up without school's input but that the protocol says they should take school into account. You can't go through observations with them scoring your child and picking out the problem areas for them not to see that the child has functional deficits in social communication. To be frank, they may have spent more 1:1 time with him than the teacher!
Thirdly, many ASD children can be more comfortable with the routine of school at times. Real life is not school with set breaks, lunch times, places to sit. It is no wonder children can appear different at times especially when they learn to follow a routine.
Fourthly, ASD teams ALWAYS hide behind panel. They are scared of doing/saying anything alone. Don't read too much into that.
Don't know if any of that helps??