We are still unsure of early K for our four year old. The school has approved but we still have concerns. Tonight I asked our son what he wanted to learn. This was the list he came up with:

How to make and explode real robots
All about the different types of snails and slugs
All about different types of reptiles
How to make really good compost and grow plants for food
Drawing and painting
All about dog breeds
How to make delicious sandwiches
More about paramecium and how they move
How to make birdhouses out of garbage
How all the systems in the body work together
More about how engines work

I thought it was interesting to get his input. Maybe we'll wait one more year on school and work on this list instead.

Is his kindyb half day or full day?

Half day.

We have had crazy number of professional weigh in on this simple question. He had two assessing psych. Psych1 thought early K was a good idea. Psych2 was on the fence. While there was no ADHD diagnosis, they had concerns about him being able to pay attention and follow instructions
Pediatrician thinks attention issues mentioned by Psych 2 are normal for young highly intelligent boys and we should try K.
OT thinks he should wait and continue with OT for sensory issues. The OT is the most familiar with our school because her kids go there and she works with some kids at school.
It should be noted that the psychologist thinks the OT and sensory issues are soft science nonsense and the pediatrician thinks the psychologists over react.
Lastly, we just had friend who is a early ed. teacher spend a week vacation with us. She thought early half-day K is a good idea for him.

A lot to consider.

Half day is easier for kids to manage, but a lot depends on the child and program. How structured is the program? How much would DS be expected to sit still, pay attention, follow directions? How much worksheets or other type work is being done? What about the other kids? Are they typically developing?

It's very hard at times to predict how a child will react until they are placed in that environment/atmosphere, but an overly structured program may backfire.

Of course, another issue is that your DS could go to K only to find out that they don't really 'learn' in K. Many K programs followed a structured curriculum today and are focused on the basics, which your DS may have already mastered. Additionally, your son may have higher expectations/abilities/skills than a K program could deliver. He may find the other kindergarteners not up to his level; and it's hard to predict what he may do or how he may react.

Sensory issues are not nonsense. They're very real. The psychologist is not being professional, imo, there; she's stating her opinion, not fact. The psychologist should let the OT speak about sensory issues and respect the field/profession.

Pediatrician is correct that attentional issues are normal for young highly intelligent boys. There's a lot of misdiagnosis of ADD/ADHD with eg/pg boys, both over and under diagnosis.

If the K program is a half day and not overly structured, I'd agree with the pediatrician that you might try it out - provided you're easily able to withdraw if things don't work out as expected.

Can I go to school with him? I like his curriculum.