Clark, L. E., and D. J. Rhea. “The LiiNK Project®: Comparisons of Recess, Physical Activity, and Positive Emotional States in Grades K-2 Children”. International Journal of Child Health and Nutrition, vol. 6, no. 2, May 2017, pp. 54-61, doi:10.6000/1929-4247.2017.06.02.1.