My children were in Montessori schools from preschool through 2nd and 4th grade. This year will be their first in traditional school. I would keep them in Montessori if I could! It is truly a wonderful curriculum and method of teaching. Some things I especially like about Montessori:
Multi-age grouping allows children to be peer leaders and helpers, and allows children to work with other children of the same ability, regardless of chronological age.
Heavy emphasis on phonics at the preschool/kindergarten level gives kids a solid foundation for reading, while the individual nature of the program allows each child to work at his or her own pace. There is no pressure, but lots of opportunity.
Grace, courtesy and practical skills are taught alongside academic skills. Grade school Montessori children, in general, are kinder and more helpful to their peers. There is less cruelty and teasing.
The individual nature of Montessori schoolwork teaches children to take responsibility for their own learning. They learn to make appropriate choices and to budget their time. Teachers guide and support the children. They provide lessons and demonstrate how to use classroom materials. They spend a lot of time observing the children to monitor progress, but they allow the children the space they need to make their own "discoveries".
The Montessori curriculum is not "dumbed down" There are high academic expectations for all the children. When my son switched to a traditional school for the last two months of second grade, I was shocked by how easy the work was. For instance, in math at the Montessori school, my son was working on long multiplication. At the traditional school, he brought home ditto sheets for 1 and 2 digit addition. Towards the end of the year, they started learning multiplication facts (usually introduced to Montessori kids in kindergarten, or first grade at the latest.) Another example is in botany. My son brought home a little book he made in the traditional school about plants. It said stuff like, "Plants need water. Plants need sun." In a Montessori class, 2nd graders would be learning the characteristics of different kinds of plants, such as cone bearing plants versus flowering plants, and diagramming the different external parts of each kind of plant. By the end of the 3rd grade, they would be able to tell you about the five living kingdoms (plants, animals, fungi, protista and monera, I think) and be able to compare and contrast the different groups for you. Anyway, I could go on and on...