I have been working in Montessori schools in Singapore and Johor Bahru since my Montessori Teacher's Training days. There is always one thing in common -- peaceful and calm learning environment. The children are usually working on their own activities quietly, and of course this comes with ground rules.
Rules are always set in the environment, but for children to carry out those rules with own willingness is quite an art. This has got a lot to do with the Montessori philosophy -- the Teachers have to carry themselves with grace. We cannot rush here or there, even when we really need to. We always need to keep our composure and be calm. Children get influenced by us. This can extend to outside the school too when Parents can keep their composure and be a role model in terms of behaviour and speech.
I do take this peacefullness in our learning environment for granted until some teachers from other traditional preschools visit our centre. The first thing that they always comment is that our centre is so peaceful and quiet. They would say children in their schools are always rowdy and Teachers always need to shout on top of their lungs to cover the children's voice to keep their voices down.
There is another reason for the rowdiness of children in traditional school settings. Children need movement, especially pre-schoolers. Since they learn to crawl, they can't wait to explore the world. Hence, it is normal for a pre-schooler not being able to sit still for more than 20 minutes. They need to move about. Montessori environment requires the children to move about to select activities from the shelves. The need of movement is fulfilled. This makes them calmer and more willing to oblige. However, in a traditional school setting, children have their own designated desks and they are required to sit there and attend lessons. The need of movement is not fulfilled and they get frustrated.
The Secret of Childhood (Maria Montessori, 1982) - This book goes a long way in helping the argument that the child-centered approach is the finest way to create great adults from children.