Three theories of egocentric speech are contrasted. Alternative predictions of the same phenomenon by the theories of Piaget, Vygotsky and a prototheoretical position associated with Mead, Flavell and Wilder are subjected to empirical evaluation. The Mead-Flavell-Wilder prototheory proved to be the most predictive. Weaknesses in its explanatory power are explored. Some assumptions remain to be tested before the contrast is complete.