Partially conflicting results from correlational studies of maternal speech style and its effects on child language learning motivate a comparative discussion of Newport, Gleitman & Gleitman (1977) and Furrow, Nelson & Benedict (1979), and a reanalysis of the original Newport et al. data. In the current analysis the data are from two groups of children equated for age, in response to the methodological questions raised by Furrow et al.; but, in line with the original Newport et al. analysis, linguistic differences between these age-equated children are handled by partial correlation. Under this new analysis the original results reported by Newport et al. are reproduced. In addition, however, most effects of the mother on the child's language growth are found to be restricted to a very young age group. Moreover, the new analysis suggests that increased complexity of maternal speech is positively correlated with child language growth in this age range. The findings are discussed in terms of a theoretical analysis of the Motherese Hypothesis; the conditions of both learner and environment in which ‘simplified’ data could aid a learner. Finally, the results of our past work, those of Furrow et al., and those of the present analysis, are discussed as they fit into, and add to, current theorizing about the language acquisition process.