Thelen et al.'s account of cognition as the dynamic interaction of processes of perceiving, reaching, and remembering within a movement planning field is a useful articulation of the Piagetian concept of sensorimotor cognition. The claim that the same kind of analysis applies to all kinds of cognition at all ages, however, is questioned in light of the distinction between sensorimotor and symbolic cognition.

Infants' knowledge need not have the same structure as the mature knowledge that develops from it. Fundamental to an understanding of number are concepts of equivalence and less-than and greater-than relations. These concepts, together with the concept of unit, are posited to be the starting points for the development of numerical knowledge.