Laski, E. V., M. Vasilyeva, and J. Schiffman. “Longitudinal Comparison of Montessori Versus Non-Montessori Students’ Place-Value and Arithmetic Knowledge”. Journal of Montessori Research, vol. 2, no. 1, May 2016, pp. 1-15, doi:10.17161/jomr.v2i1.5677.