This chapter shows that constructing and maintaining more complex and numerous representations on which a growing repertoire of processes operates more and more smoothly and efficiently with age require a working memory of increasing capacity. Time-Based Resource-Sharing (TBRS) developmental role is best exemplified by the extensively documented impact that working memory has on learning and academic achievement. The pivotal role that working memory plays in development probably explains the and widespread enthusiam that working memory training elicited in developmental psychologists. The most natural way of theorizing development within this perspective was to imagine that changes mainly occur in the capacity to process information conceived as a 'given', and not as something to be constructed as in Piaget's theory. Of course, important aspects of development that are crucial for cognition such as sensorimotor development in infancy might be difficult to account for by some increase in working memory capacity.