Laurel gave an excellent reply. My program is heavily inspired by the Montessori approach. I also take from Reggio too but my first intent was Montessori.
Here is a great FAQ's page that answers a lot of what you are asking.
http://www.montessori.edu/FAQ.html
You can also do a lot of reading on line and there are tons of sites, blogs and pages that teach and explain how to incorporate Montessori practices into a multi-aged group setting.