Jean Piaget was a forefather of modern child development theory. Surprisingly, this educational academic began his career in the natural sciences. A quick turn to psychoanalysis brought an interest in human learning and knowledge acquisition. Piaget’s stages of cognitive development encompass growth from birth through adolescence. They include what he termed the sensorimotor stage (birth to 2 years), the preoperational stage (approximately 2 through 7), he concrete stage (7 through early adolescence), and the formal operational stage (adolescence). Educators can use the developmental theories behind each stage to create age-graded strategies for teaching mathematics.