One hundred and fifty years after Maria Montessori’s birth, tens of thousands of teachers around the world still hail her innovations and educational philosophy. One of Italy’s first female doctors, Montessori applied her training as a scientist to teaching children in new ways. She upended conventional thinking about education by, among other things, letting kids freely choose from an array of classroom activities to foster their independence.

Many of Montessori’s original ideas are commonplace today, especially in preschools and kindergarten classrooms: child-sized tables, hands-on games and other opportunities to play at school. Even the common practice of letting children sit on the floor was revolutionary when Montessori allowed it in her first school in 1906.