Research Findings: Mental state verbs (MSV), a component of literate and academic language, may facilitate vocabulary growth, as they relate to metacognitive and metalinguistic awareness as well as decontextualized talk, all of which have been associated with vocabulary growth. In this study, we examined teacher MSV use in group content instruction and book reading in Head Start classrooms (N = 49) to determine the prevalence of teachers' use of MSV. We sought to determine whether there was an association between teachers' MSV use and children's (N = 402) receptive and expressive vocabulary scores across 1 year of preschool. Results from hierarchical linear modeling revealed that teachers' use of MSV in group content instruction was positively associated with children's end-of-year receptive, but not expressive, vocabulary scores. No significant relations emerged for book reading. Positive associations between MSV in which the child was the referent of the verb and children's receptive vocabulary were found, which indicates a potential scaffolding effect. Practice or Policy: Results indicate that teachers should consider including MSV in their content-rich instruction and provide support by placing the child as the referent of the verb. Additional instructional implications are addressed.