Examining how fidelity to the model impacts outcomes, this experiment looked at 3 classrooms which supplemented Montessori materials with other materials such as puzzles and games. Supplemental materials were removed from 2 of the 3 classrooms, and the students in those 2 classrooms showed significant growth in early reading and executive function along with greater growth in early math than in the classroom with supplemental materials
Journal of Montessori Research Spring 2016