Maria Montessori's groundbreaking research on "sensitive periods" in children's development shows that when they are intensely interested in a certain type of learning, they master it with much greater ease and speed than would be possible at another time. This is a foundation of Montessori education.
Another is the fact that young children learn best by using their hands, not by looking or listening, so the Montessori materials are developed with that principle in mind. The lengthy work period in the morning develops the young child's concentration and focus in a natural, unforced way. The close attention paid to each child's interests and needs sometimes means that a child will begin reading or writing quite early; however, it's a myth that Montessori education "pushes" early academics. Each child develops according to his or her own natural rhythm.