This article argues that children's difficulty with passive constructions is related to properties of the by -phrase. Specifically, we argue that children are in full control of all aspects of the passive construction except for the ability to transmit the external θ-role of the predicate to the by -phrase; we thus reject Borer and Wexler's (1987) claim regarding the maturation of A-chains. Our conclusion is dictated by the results of an experiment we conducted, and supported by data already present in the literature.