“This neat picture of successive stages has aroused such strong positive and negative reactions that the ensuing debates have obscured Piaget’s really important contribution: His description of different ways of knowing is far more important than quibbling about whether they neatly follow one another chronologically. And what is especially important is the description of the nature and the development of the middle stage of concrete operations. This is the task to which he devoted the greater part of his mature life and the topic of all but a handful of the more than one hundred books he wrote about how children think in a staggering range of domains, including logic, number, space, time, motion, life, causality, machines, games, dreams.”
Papert, S. (1993) The Children’s Machine: Rethinking School in the Age of the Computer. NY: Basic Books. Page 153.