Research-supported knowledge about how children develop language is considered foundational for high-quality instruction and as such, measuring and developing teachers' knowledge has been emphasized across the field of early childhood. However, there is a critical gap in understanding how this static knowledge gained through pre-service and in-service experiences is connected to enacted practice. To address this, we compared teachers' static knowledge regarding language development as assessed via a traditional paper and pencil measure with their knowledge used in-the-moment during language interactions with children via stimulated recall interviews. Ten educators from a variety of early childhood programs completed the surveys and participated in two stimulated recall interviews about language interactions with children. Interview data were coded for emerging themes regarding knowledge use and then compared with the knowledge assessed on the static measure. We found that overall, teachers had high levels of research-based knowledge regarding children's language development and that this knowledge was part of their in-the-moment knowledge use; however, it was used infrequently. Educators tended to utilize knowledge about their context more frequently than knowledge from the field (formal sources of knowledge). Implications for measuring knowledge, professional learning, and supporting the use of knowledge in practice are discussed.