Traditional classrooms are made up of children born within one year of one another. In such an environment, your birthday is your destiny: if you are the youngest child in your class, you will always be the youngest. Children in Montessori classrooms are grouped in mixed ages and abilities in three-year spans: 3-6 and 6-9. Children who were once among the youngest in the class will, in two years, be among the oldest. As in a family, this allows children to try on different roles and to learn from one another, not just from the teacher. There is constant interaction, problem solving, child-to-child teaching, and socialization. Children are challenged according to their ability.