Montessori Groupings:
 
The levels usually found in a Montessori School correspond to the developmental stages of childhood:
 
Early Childhood:

Absorbent mind stage (ages 3 to 6)

Junior Primary:

Social and imaginative stage (ages 6 to 9)

Senior Primary:

Social relationships and moral justice (ages 9 to 12)

Middle School:

Trust, self-expression and contribution to society (ages 12 to 15)

High School:

Analytical thought, commitment and responsibility (ages 15 to 18)