J.,
if you think you're interested in private schools, you'll want to start looking around about now. I'd just get an idea of what's around and the places that you believe might be good for your family. Talk to people who have looked at private schools too, as they can provide a wealth of information. Do you want your son to go to preschool at the private school as well? Many do have 3 and 4 year old programs, so that's something to think about. Anyway, there's quite an application process and you'll need to get started on that late fall of the year before he'll attend. Usually the application deadlines are around the end of January. Most schools do have rolling admissions, but it's better to be one of the first to apply.
It's great that you're thinking of this so early. We are just now applying for my 5 year old for next fall. We didn't think we'd be interested in private schools, but he's been in public kindergarten and after this year we really want to get him into a private school. So we're late in the process but hopeful that he'll get in.
Good luck!
K.