Wevecome my DD was also diagnosed at her first appointment (with a paed), although the official diagnosis came only after the appointments with the SALT and psych, months later.
We were very lucky with how easily we got DD assessed and diagnosed, for which I am hugely grateful. So whilst I know that the tally of professionals listed by zzzzz is the norm for most diagnoses, it isn't necessarily the case for all.
DD's nursery flagged up issues and did some 'special measures' stuff with her - small group work to improve her socail communication and compliance, but no mention of formal assessment/diagnosis. No issues were flagged up by any of the three schools she attended (though there clearly were some issues, still), in fact the (lovely) second infant school she attended put her on the G&T list. I took her out of school in Y4 (2nd year of junior) to home ed her, because she wasn't happy at school any more and I didn't feel that they were meeting her needs. I think that ultimately made it easier to get her assessed and diagnosed a year or two later, because because I didn't have to push a school into organising that. So my tally of professionals was:
Visited GP with a list of concerns and asked to be referred to a developmental paediatrician. He was a new GP, just qualified (I was asked to complete a feedback form about him afterwards), and initially he told me that the school would deal with a referral. When I told him she didn't go to school, he was clearly very shocked (he wasn't English), and then tried to cover up his shock. He asked what I wanted him to do, and I told him which hospital and dept. I wanted the referral to go to. I think if I'd said the prime minister he'd have referred me, at that point.
So, GP 1
Appointment with developmental paed came through months later. We had a couple of hours with her. No forms or anything, she just talked to us - especially to DD. I'd been convinced I'd be laughed out of the office, because on a good day, you'd never in a million years think that DD is autistic. She knew just the right questions to ask, though, to get to the relevant stuff. She was amazing. ❤️ So, at the end of that appointment she gave us a verbal diagnosis of Asperger's, contingent on the SALT and psych agreeing. 2
Saw the SALT a few months after that. Very uneven profile on the tests. Scored very well in certain areas (that you wouldn't expect with ASC) but low on others. 3
Saw psychologist a few months after that. Again, no forms or anything, she just talked to DD. DD was anxious in that appointment, so her aspie behaviours were much more obvious than at the other appointments. Psych confirmed the diagnosis. So, total tally 4.
I know that we were very lucky and that this is an unusual trajectory.