This study concerns the acquisition of complex sentences with perception and epistemic verbs that take a second verb in their complements. The acquisition of complementation began between two and three years of age in this longitudinal study of four children's spontaneous speech. The results of the study showed that (1) complement types and complementizer connectives and (2) the discourse contexts in which complementation occurred were specific to individual matrix verbs. The most frequent verbs acquired were the perception verbs see and look and the epistemic verbs think and know. Developments in both discourse and syntax indicated that these verbs expressed attitudes of certainty/uncertainty toward the content expressed in their complements. The results are discussed in terms of both linguistic and psychological factors in the acquisition of complex sentences with complementation.

Acceleration and variation about this trend are consistent with maturational models of language acquisition. With an empirically sound characterization of early variation in morphosyntactic growth rates, future investigations can more rigorously test hypotheses regarding biological, environmental, and developmental contributions to the acquisition of morphosyntax.

There is sequence and simultaneity in development that no prior framework has fully explained, as well as evidence of cross-morpheme relationships. In this article, the authors interpret these findings as support for the gradual morphosyntactic learning hypothesis ( Rispoli & Hadley, 2011; Rispoli, Hadley, & Holt, 2009).

The sentence production capabilities of young children undergo major changes during the same period in which grammar develops. This article reports data from a cross-sectional sample of 52 children between the ages of 1;10 (years; months) and 4;0, and looks specifically at the dichotomy between stalls, sentence disruptions that are the result of glitches in sentence production, and revisions, sentence disruptions that involve self-monitoring and the rapid replacement of words or morphosyntactic alternatives. It was found that revision rate increased with level of grammatical development, but that stall rate was not related to grammatical development. These results indicate that children's capacities for self-monitoring and maintenance of multiple linguistic alternatives increase during the period of grammatical development.

The findings provide evidence that input informativeness, an abstract and distributed property of input, contributes to morphosyntactic growth.