My son is turning 4 in July and has been attending a Pre-K program for kids who've received early intervention treatment. At around 18 months, my wife & I noticed that he wasn't really speaking much. My wife is a stay at home mom, so we attributed it to us catering to his every need. He understood what we said to him, he learned shapes, colors, letters, numbers, all before actually speaking words. It was mostly jargon.
We had him evaluated for speech therapy via early intervention and we began to see improvement in his speech. The therapist then suggested that he may be on the autism spectrum, particularly because he would spell the words he wanted to communicate to us if we could not understand him verbally. She also mentioned that he tended to "stim?!?" by spinning in circles if overstimulated.
At her suggestion, we enrolled him in a pre-k class with other such children and he has shown vast improvement in speech. He talks constantly, he was reading, writing, counting and spelling before joining the class, it was his speech we were concerned about, not realizing that in other areas he was advanced for his age group. We were mainly focused on the milestones he didn't meet which was social interaction and speech. Again, we assumed that this was because he was home with my wife and that's pretty much all he knew.
While at his pre-school, I do notice that he will "hover" around the other kids. He would watch and observe, but appear to be too shy or not know just how to invite himself into the group. Once he is accepted into the group, he does quite well, no tantrums or violent episodes that we've noticed or the teachers have notified us about. Just being in the school has opened him up to being more receptive around large groups of people, which prior to that would cause him great anxiety initially. He hasn't been formally diagnosed, in your opinion, what does his behavior indicate?