I can understand why you are worried, because at 3 years old, some assessments can look different as the child grows and develops. It might be worth going back to the NUH team and asking them directly whether a follow-up review is recommended down the road, since developmental profiles can sometimes become clearer with time. Even without an Autism or ADHD diagnosis, the behavioural concerns your teachers flagged are still real and worth addressing, so do ask the doctor whether he can still access any support programmes based on his current profile. Getting a second opinion from another developmental paediatrician is also a reasonable option if you feel unsettled, because peace of mind matters too and it is better to explore all avenues now while he is still young.