Psychologically, she observed the "herd instinct", or the tendency to work and socialize in groups, as well as the powers of reason and imagination.
The second plane of development extends from around six years to twelve years old. During this period, Montessori observed physical and psychological changes in children, and she developed a classroom environment, lessons, and materials, to respond to these new characteristics. Physically, she observed the loss of baby teeth and the lengthening of the legs and torso at the beginning of the plane, and a period of uniform growth following. Psychologically, she observed the "herd instinct", or the tendency to work and socialize in groups, as well as the powers of reason and imagination. Developmentally, she believed the work of the second-plane child is the formation of intellectual independence, of moral sense, and of social organization.[39]