Jabarkan Seifer, Calvin "Educational Psychology" dari Teori perkembangan kognitif

Geary, D. C. (2004). Evolution and cognitive development. In R. Burgess & K. MacDonald (Eds.), Evolutionary perspectives on human development (pp. 99–133). Thousand Oaks, CA: Sage Publications. Teks selengkapnya

Wagner, K. V. Background and Key Concepts of Piaget's Theory