One significant advantage of a mixed-age classroom is the ease with which each year begins. Montessori three-year loops, in which ages 3 to 6, 6 to 9 and 9 to 12 form single classrooms, allow two-thirds of a class to return to the same teacher at the start of a new school year. Teachers spend less time teaching classroom procedures and more time teaching subjects such as math and English. This is due to the presence of older peers who act as role models and remind younger students how to do their work and behave appropriately in class.
The mixed-age classroom is a more natural and realistic environment than the typical public school classroom, in which everyone except the teacher is essentially the same age. Not many adult workplaces form cohorts of people born in the same year. Rather, in a child's future career, she will be surrounded by people of many different ages. The mixed-age groups in Montessori schools are a good place to become familiar with such an environment.
The child, rather than the teacher, is the primary focus in Montessori classrooms. One result of mixed-age instruction is that the child concentrates on her own learning and not on the teacher. Often, simple questions about a child's work can be answered by one of the older students in the classroom, who has likely already done such an assignment. This means that the student does not have to waste time waiting for a busy teacher to have a chance to hear his question.
When students are thus empowered to solve their own problems, the teacher is allowed to focus on students who are experiencing significant problems understanding their work. The older children are not assistant teachers but rather mentors for the younger children. Already capable students become independent and self-motivated, and teachers are able to invest more time in helping struggling students.