Try not to worry too much--you have options. A benefit to your son's profile is that you can explain that the academic pieces come easily (a plus to a teacher who has students at so many ability levels), but the social learning has to be taught more directly.
There's not K class in existence that could meet his academic needs, but a caring teacher can help him feel safe and secure at school.
And you're not stuck! I bet you're carrying a lot of anxiety with you into any classroom situation and are looking for potential disaster, and just...overwhelmed with worry. Keep telling yourself--this is not the first or last decision you'll be making about DS and you have the freedom to change your mind.
