I have to second the call for play-based pre-K - and keep it short, so your DS can continue his learning at home, if he so desires.
My favorite pre-K story: DS, then 3, was at play based pre-K and the teacher served Popsicles as a special treat one day. The teacher enjoyed conversing with the students while they ate their snack, as this was a structured "social time" for the class. Apparently, the Popsicle sticks had "jokes" on them...well, DS decided to "tell the joke" to his pre-K class. Except, the teacher noticed he was READING the joke from the Popsicle stick. She was STUNNED, and sent that stick home in a plastic bag informing us of what had happened). We were not surprised (DS could read whatever he wanted to, by this point).
Actually, the funniest part was DS's little pre-K friends handing him anything that needed to be read, since they'd all figured out that he could "crack the code" (useful when playing video games with "tip manuals"), etc.
It will be OK. BTW, don't have much higher expectations for academics in a typical kindergarten, or you might be disappointed.
