Yes, talk to the school.
I guess I’m worried he’s going to get labelled as the naughty/difficult kid by the teacher or other parents before he’s even started
^ Exactly why you need to open the conversation with them as soon as you can. Let them know that he is on a waiting list for a social, communication assessment.
Whilst he has been at Nursery, has he had support plans in place? Have they been differentiating for him ? Have they been putting strategies in place to help him ?
The more the school know about what has been tried and what works / what doesn't work for the child, then the transition is going to be so much easier.
Nursery have said they’ll talk to the school to explain the situation. I’ll ask them when that will be and what they’ll say. Would I be able to see a copy of any report they give?
Yes, you can ask to see anything they have on record for him, but it is most likely they will be having conversations about him, verbally.
Also for the paediatrician appointment, I’ve read other threads where people have said about passing on SALT and Ed Psych reports etc but ds hasn’t had either. Is there anything I can do/prepare to get the most out of the appointment?
Ask the Nursery to complete a developmental profile and take a copy with you.
Jot down a list of things that you notice, or that you think your ds might do slightly differently from his peers. Wherever possible, try to use 'measurable quantities'..... so rather than 'doesn't sleep well' , note when he sleeps, when he wakes, what an 'average night' looks like.
Try and think about things you might do, which might have become every day for you now, to accommodate him, or to avoid him being upset.
Think about different areas of development - what is his speech like, his understanding, his eating, his sleeping, what happens when he goes somewhere new?, what about his play? - what does he play with, does he use things and pretend they are something else, what happens if someone joins hi in his play, etc. etc. Do noises bother him or different textures, etc etc
Is that relevant? Will they have those notes?
First appt should take a full history. You'd like to hope so, but never assume - always tell them twice rather than not at all.