What factors influence children's understanding of language, in both typical and atypical development? In this article, I summarize findings from the Longitudinal Study of Early Language (LSEL), which has been following the talk, understanding, and interactions of typically developing (TD) children and children with Autism Spectrum Disorder (ASD). The LSEL has found group similarities in syntactic understanding and word learning strategies, but also within-group variability that correlates with other aspects of the children's behavior. In particular, early linguistic knowledge and social abilities are both shown to play independent roles in later talk and understanding. Thus, theoretical perspectives that highlight social vs. linguistic underpinnings to language development should be viewed as complementary rather than competing.