Ages 5-6 years

By the end of kindergarten, the Montessori children performed better on standardized tests of reading and math, engaged in positive interaction on the playground more, and showed advanced social cognition and executive control more. They also showed more concern for fairness and justice.
Lillard A, Else-Quest N.
"The early years. Evaluating Montessori education." Science. 2006 Sep 29;