Montessori is a quasi-meaningless label at this point, I believe, though perhaps you can get an accreditation? I think the Waldorf label is much more tightly controlled.

It is unquestionably a core part of Waldorf philosophy to believe that children who learn to read before losing their first teeth are unbalanced and living too much "in the head." There is a really complex philosophy and the teachers all go through a long and exhaustive training that IMO is hostile to children who develop asynchronously. I vaguely considered sending DS to a Waldorf preschool--I didn't at all care if he was taught anything about reading or math at preschool--but could not reconcile myself to the idea of sending him someplace where his basic mode of development was going to be viewed with suspicion or seen as inherently dysfunctional.