Conversation with the parents may highlight autistic behaviours at home that the pupil is able to control at school. This was certainly the case for my very bright daughter when she was diagnosed with Aspergers aged 8. In fact the psychologist who observed her in school was told by the teacher there was “nothing wrong” with her (also correct, she is different, not faulty) but listed 10 autistic traits he noted within 10 mins of entering the room. This difference between home and school would be uncovered through the detailed discussion required for a comprehensive EHA, you would then think about the causes of the behavioural difference (but please, with an open mind – many autistic children ARE completely different at home to school).
We see GPS asking us to do Single Point Of Access referrals to Neurodevelopmental Pathways constantly, because we spend so much more time with pupils. As social care ask us to do EHAs. We also have a lot of children with attachment or other parenting problems that can look like ASD / ADHD.
A bright pupil who can’t sleep yet/ or is excessively tired might in fact be anxious, suffering from a mental health problem, or have a sleep disorder (like sleep apneoa or narcolepsy). They could have a sleep problem caused by ADHD or ADD, or maybe they play Fortnite all night and throw a tantrum when told to stop and parents think this is an autistic meltdown, and not a parenting issue. I think your EHA should illuminate this further.
If you do refer for ADOS, it is just a referral – it is up to medical professionals to decide if the pupil is in fact autistic.