My daughter is 10 and diagnosed with ASD (Asperger's). We just got the diagnosis this year. Oh how I wish that it had occurred to me or anyone else for that matter, that DD had autism when she was four. That time was so difficult for me. I thought maybe I would share some of the behaviors that she had at that age. Looking back, it seems clear that she did have autism, but many are still very uneducated about autism and its symptoms. I do a lot of self-blame regarding her delayed diagnosis. There are a lot of things that can be done as early intervention that will allow your son to enter school with minimal difficulty. Without them, you could be looking at years of OT, PT, speech therapy (for pragmatics) and other delays that will keep him from performing his best in school. I would not worry that your son could be wrongly diagnosed, there is a fairly high bar for diagnosis and a physician or psychologist trained in diagnosing ASDs should be able to differentiate his symptoms. I am not saying that kids aren't misdiagnosed, just that it probably doesn't happen that often. Trust your gut at this stage, if you are noticing symptoms, keep a journal and note how often they are happening. That will be extremely helpful to anyone working with your son. DD symptoms at 4:

1. Explosive tantrums (daily)
2. Inability to share or play in group setting, need to control play
3. What the daycare described as "eloping" from classroom when stressed or upset
4. Sensory issues with food, sound, touch (only eating a handful of foods, sensitivity to noise and loud places, not liking to be touched unless it was on her terms)
5. Hyperlexia, DD started talking at 5 months and could speak in full sentences by 12 months. She started reading sight words @ 2 and independently reading books at 3. Most consider this a splinter skill for spectrum kids, but DD is highly gifted fwiw.
6. Motor skill delays, both gross and fine motor. These delays trended throughout elementary school. Don't listen to those that tell you your child will grow out of it! They most likely won't without some assistance. Any speech, language, and motor skill delays will need therapy to correct.
7. Rigid, unyielding personality with inability to transition from activities. I know a lot of PG kids do this. However, this along with many other autism symptoms is a red flag. On its own, it is probably just a function of high IQ.
8. Narrow iterests and focus
9. Constantly interrupting or talking over others. Not necessarily a red flag if it happens only occasionally, but if it is all day, every day, then you can see a pattern of behavior.
10. Echolalia...I had no idea what this was until she was diagnosed. DD would memorize commercials, lines from her favorite movies and t.v. shows and repeat them ad nauseam. I was proud at first that she had such a good memory!
11. Ritually stacking or lining up objects during play. I would not be concerned if you see this once or twice, but consistently doing this is a symptom of autsim.

I would agree with those that said their child was happier and better adjusted after diagnosis. Teachers can be very judging, and some of the symptoms of autism can be interpreted as the behavior of a bratty child. Realizing that these behaviors stem from a disorder will help those around him understand and work to improve his behavior. I wish you luck on your journey!