Educators' language and literacy knowledge is considered important for informing classroom practices and thereby supporting children's early language and literacy development. This includes both disciplinary content knowledge (knowledge concerning how oral and written language are structured and map to one another) and knowledge for practice (knowledge of effective strategies and practices for supporting early language and literacy). In this study, we examined the associations among 485 early childhood educators' content knowledge and knowledge for practice, their observed language and literacy practices, and the emergent literacy learning of 2004 children enrolled in their classrooms. We found significant, positive correlations between measures of educators' content knowledge and knowledge for practice and classroom practice, indicating that early childhood educators with greater levels of knowledge tended to exhibit more desirable classroom language and literacy practices. We also found significant, positive associations between educators' knowledge and children's print concept, letter naming, and phonological awareness learning, but not children's oral language learning. The associations between educators' knowledge and children's print concept learning were mediated by classroom practice. Together, these results reiterate the importance of educators' language and literacy knowledge and also provide some support for practice as the mechanism through which knowledge relates to children's learning. © 2019 John Wiley & Sons, Ltd.