Maria Montessori (1870 - 1952) was an Italian educator who developed an educational system based on child development. Her schools deal primarily with preschool and early elementary aged children. Her method is characterized by an emphasis on self-directed activity on the part of the child and clinical observation on the part of the teacher. The learning environment must be adapted to the maturity level of the child. New concepts are taught using autodidactic (self-correcting) equipment). In this way a child's mistake is caught immediately instead of the child doing an activity and not getting feedback until a later time. Montessori teachers stock their classrooms with nature shelves, living plants and small pets, or perhaps a window sill garden, allowing children to experience as much of the natural world as possible given modern constraints. The class may have a three year age span thus allowing for ranges in development and social levels. Spontaneous Activity in Education covers a wide range of topics from child development, to setting up a classroom and training teachers, social issues, and educational philosophy.