Montessori classrooms for children from 2½ or 3 to 6 years old are often called Children's Houses, after Montessori's first school, the Casa dei Bambini in Rome in 1906.
Elementary school classrooms usually serve mixed-age 6- to 9-year-old and 9- to 12-year-old groupings; 6- to 12-year-old groups are also used.