Behr MJ, Wachsmuth I, Post T. Rational number learning aids: transfer from continuous models to discrete models. Focus on learning problems in mathematics. 1988;10(4):1-18.This paper is concerned with how well children who have head instruction about rational number concepts based on a continuous manipulative aid are able to transfer their knowledge to accomplish tasks based on a manipulative aid which can be interpreted as discrete. The aid used was an egg carton which, if the subject views the holes as salient, is discrete; if, on the other hand, the subject focuses on the proportion of total area enclosed by the edges of each of the holes, then it is viewed as a continuous entity