We have to first differentiate method from philosophy po.
Method, or pedagogy, determines how the school conducts its classes or teaches the students. This is where we commonly have people referring to their schools as either progressive or traditional. A more extensive discussion of the difference between the two methods are found in http://tinyurl.com/36lunos
. But suffice it to say that the main difference in the two is in the focus of education: in traditional schools, the teachers and the curriculum remain the focus (teacher-centric), and the students have the burden placed on them to keep up; whereas in progressive schools, the student/learner's unique (as much as possible) needs and paces are taken into greater consideration and much more individualized learning should ideally take place.
The hallmark of a true progressive school is not in its facilities or curriculum (so whether or not your three-year old can do fractions, or your five-year old understand the nuances inherent in a monocot and dicot plant shouldn't matter) but rather in the amount and level of personal interaction and involvement that your child's teachers are able to engage them in. A true progressive school is able to actively stimulate the child's natural thirst for knowledge, and is able to satiate that thirst appropriately. The curriculum and the facilities are tools which if used in conjunction with great and effective teachers are able to create a environment that provides a fun learning experience.
Based on this definition, there are "big" schools that are progressive, and there are small schools which are "traditional". But more often than not, because of the economies of scale and cost, smaller schools are progressive schools. But, again, not all small schools (whether these are preschools or grade schools or high schools) are progressive.
Now, the reason why most progressive schools are expensive is because they tend to have the best teachers, and they have to invest in their teachers' education and training. The difference in the program between progressive schools and traditional schools is like the difference between a gourmet hamburger and one from a fastfood: both sandwiches have the same basic content (buns, burger, some garnish) but the difference lies in the preparation, execution, add-ons and presentation of the sandwich.
Now, the philosophy of the school/learning center/institution is the one which guides and instructs the program and the execution of the curriculum, the "method". So it doesn't necessarily also follow that all "montessori" schools are progressive (but I believe all true Montessori schools are progressive), much as it doesn't follow that all traditional schools use outdated / in-appropriate means of education.
There isn't one sure-fire way to educate a child, that's why the better schools recognize that they're best served to be able to use and adapt the best features of the different theories around. For the record though, I have to say that I believe ALL schools should have developmentally appropriate practices/procedures for their children. That's non-negotiable for me. It's like saying you have a chair without a backrest - that's a stool now, not a chair.
All the other theories floating around: Reggio Emilia, Multiple Intelligences, Waldorf, Montessori, Bank-Street, eclectic (just means a mix of whatever; but, if this doesn't have a focus or hinge turns out to just be a big messy jumble of ideas) are theories and philosophies that guide how the preschools implement their program of education.
Good luck in your search to find a school which fits your child's temperament, learning style and personality!