My experience was years ago so no doubt very much out of date now. Just in case it's of any use though, the first appointment was about the Paed gathering as much information as possible about the child's history and behaviours.
Questions asked were things like:
- What was the birth like? Any problems?
- Any family history of medical issues?
- Child's medical history?
- Any issues with motor skills, speech, behaviour etc?
- When did you first notice problems?
- Do they go to nursery/preschool/school and how are they getting on?
I would make yourself some notes on the above as sometimes your mind tends to go blank and then you kick yourself later for forgetting...
While all this was going on, the Paed was observing DS to see how he interacted with the people in the room and the toys that had been set out for him.
I remember that DS was also weighed and measured, including his head size.
In our case the Paed agreed that DS needed a full assessment. For us that meant a week's worth of appointments with the OT, Physio, Child Psych and a SALT. They also wrote to the preschool, DS' SALT and our portage worker for their opinions. Different parts of the country will have their own system for this, and it may be very different for you.
The assessment itself took place around 3 months later. It was at short notice though so might possibly have been the result of someone else having to postpone/cancel their appointment.
At the end of the assessment there was a meeting for everyone involved to attend. The HV and preschool didn't bother, so it was really just us, our portage worker, our SALT, and the people involved in the assessment. During that meeting the Paed listened to everyone else's opinions, looked at their results, and then diagnosed ASD.
As I say though, this was a long time ago and probably a different system. I would imagine the questions asked at the first appointment would still be the same though.
Good luck. 