Dr. Montessori organized her student groupings in multi-age classrooms. The age breakdowns are as follows: 3-6-year-olds in Primary 6-9-year-olds in Lower Elementary 9-12-year-olds in Upper Elementary 12-18 year-olds- Adolescence 18-24 year-olds- Maturity     AMI article on Planes of Development You Tube video on Planes of Development If you haven’t ever seen a multi-age classroom in action, it can seem…