1. Airasian, P., & Bart, W. M. (1975). Validating a priori instructional hierarchies.Journal of Educational Measurement, 12, 163–173.
2. Case, R. Marini, Z., Mc Keough, A., Dennis, S., & Goldberg, J. (1986). Horizontal structure in middle childhood: Cross domaine parallels in the course of cognitive growth. In: I. Levin (Ed.),Stage and Structure (pp. 1–40). Norwood, N.: Ablex Publishing Cy.
3. Connor, F. P., & Talbot, M. E. (1966).An experimental curriculum for the young mentally retarded children. New York: Teachers College Press.
4. Demetriou, A., & Efklides, A. (1987). Experiential Structuralism and Neo-Piagetian theories: Toward an integrated model.International Journal of Psychology, 22, 679–728.
5. Dumont, J. J., & Kok, J. F. (1973).Curriculum Schoolrijpheid, deel I (Curriculum Schoolreadiness, Part I). Malmbergh: Den Bosch.