Children have to be educated, but they have
also to be left to educate themselves.
~Abbé Dimnet, Art of Thinking, 1928
One thing I look for is the AMS, The American Montessori Society. Teachers usually have evidence of their training posted in their classroom and know who the AMS is. A seasoned directress knows how to use and instruct the children.
With any good quality early childhood program, check it out thoroughly.
One very dedicated Montessori teacher that has really touched my heart has been Ms. Mars. I urge you to check out her blogsite on blogger;
Montessori in Mars
You'll get the idea of what Montessori is about on her site.