Research Findings: The current study examined whether collective small-group behavioral engagement and teacher behavior management during small-group instruction predicted print knowledge, phonological awareness, letter writing, and expressive vocabulary gains for preschoolers at-risk for literacy difficulties. This study, part of a larger project, included 23 teachers delivering a small-group literacy intervention to 75 preschool children identified as at-risk for literacy difficulties. Hierarchical linear modeling results revealed that collective small-group behavioral engagement was predictive of child expressive vocabulary gains (d = 0.13), but teacher behavior management was not a significant predictor. Practice or Policy: The results demonstrate that high levels of collective small-group behavioral engagement during small-group literacy instruction contributed small positive effects to preschoolers' expressive vocabulary skills. As many small-group interventions are intended for children at-risk for literacy difficulties, these results are promising because preschool children at-risk for literacy difficulties appear to benefit from the intervention when collective small-group behavioral engagement is high. Including activities that prompt strong child engagement may be a critical factor in realizing the full potential of small-group literacy instruction in young children. [For the corresponding grantee submission, see ED629742.]