I think the way to start is by really thinking about what you want your son to experience now. Is it really important that he learn to sit still and listen at 3 (or at 4)? Is it important that he is given schoolwork that is challenging? Is it important that he have time to run & play with other kids? Is it important that his teachers accept him for who he is? Is it important that he not be exposed to superfluous education (e.g., relearning the ABCs)?
I'd start by figuring out what is non-negotiable to you, and then what you'd prefer and go from there. You might find that it's not the philosophy that matters as much as the way an individual school or teacher applies it. And you might find that a play-based preschool is what your kiddo needs for now.
