V was 4 when he had a psycho-educational evaluation and seperate speech and Occupational Therapist (OT) evaluation. I could not find one clinic to handle all the testings... so I had to get seperate professionals, but at the end I got a pretty good idea of what is going on.
As far as Sweet Pea, EI tested her whole development through a screening and then only did the actual test for speech as it is her problem area.
To be honest, I don't regret having V tested, but the psycho-educational evaluation did not reveal anything I did not know already... The Occupational Therapist (OT) was the big one for us, and then speech/audio as he has Auditory Processing Disorders (APD).
We are now waiting for Autism Spectrum Disorders (ASD) testing specifically (loooong waiting list).
Even with testings, it's not a perfect science. Sometimes, kids have a clear cut diagnosis, but most of the time it is a lot of trials and errors. The younger the child is, the harder it is to really find a diagnosis.
In the mean time, even if there are still lots of ?, you can still identify some lagging skills and work on them or compensate the difficulties. Does your little one have issues with calming down: read about calming techniques (calming music works really good for my kiddos), weighted items, etc. Does he have problems remembering things: make it visual. Expressing feelings with words: read about feelings, act the feelings for him and make him participate, (that's a VERY hard one for V... still not successful at it. I kind of put it in the back burner for now).
What did your pediatrician suggest?