Maria Montessori was the one of the first female doctors in Italy. In 1907, she began her first Casa de Bambini or Children's House. Everything in the classroom was designed for a child to learn from. Montessori was a great observer. She observed the children in her care. In her observations she noticed that children enjoyed doing real work --- sweeping with real brooms, using real cups and plates, and preparing their own food.
She also noticed children have sensitive periods for learning. Sensitive periods are times in a child's life when he or she exhibits rapid growth in development of one particular area. Children from 2.5 to 8 go through several sensitive periods. The Montessori classroom uses the sensitive periods as a foundation in its perspective: language, order and movement. The Montessori philosophy of education has since spread around the world. It emphasizes following the child as he learns through doing things himself.
You can learn more about Montessori through the American Montessori Society