Hi Annette,
Be careful what you wish for!
It's not that PG kids don't like teacher-directed learning, it's just that teachers of 3 year olds don't typically offer learning that is useful to a PG kid.
Be glad that he enjoys self-directed learning, some PG kids don't and end up with 'no learning at all!' Not really, but wouldn't you rather a child learn academics in a self-directed way than throw all that intensity into becoming the best at playing 'Pokemon Video Game?'
There is no way to predict the future for kids who are so far outside the norm. It's great that someone introduced you to the idea that homeschooling might be manditory - but it's way to early to know.
It's great that the school has opened their kindergarten class to your child, and if it's a half day program it might be a great place for him to learn about social skills. I don't think you should expect much from him socially - he is so young - as long as he isn't harming anyone, and is enjoying himself, and still has energy to learn when he gets home, that's as much as one can hope for.
In other words, don't prep him - let the experience come - there is no way you can create a positive reinforcer as great as a room full of kindy classmates.
What happens when you 'play school' and let him be the teacher to a bunch of stuffed animals? Do he have an basic idea of 'class rules?' (Is he potty trained?) Does he know to wash his hands before returning from the bathroom? Can you set a timer for 5 minutes and practice raising one's hand and waiting to being called on before speaking? You could play along - that would give you an idea of how much eye contact he is giving you, and how able he is to 'pause' when he wants to talk.
Try and visit a classroom with kids of similar age to the ones he'll be meeting and see what kinds of rules are in place, and what the room is like. It may be louder than he is used to, so visit loud places and practice 'loud survival.'
I don't think the kindy teacher will mind if he is off doing his own thing at the begining of the year. She will expect children not to know how to 'do school' and see it as her job to prepare them for 'real school.'
I can't tell you the times I've 'overprepared' my DS15 because my standards were way way way too high. Opps!
Love and more love,
Grinity
