Research Findings: A growing emphasis in the literature on children's self-regulation signals the need for increased understanding of the ways in which young children become active players in the acquisition of knowledge. In particular, self-regulation may be linked to subsequent academic achievement through greater engagement with the learning tasks and activities made available in the preschool classroom. This study tested preschoolers' (N = 603) observed task engagement in the classroom as mediating the relations between directly assessed self-regulation and changes in their language and literacy outcomes during the preschool year. Findings indicate that self-regulation is directly related to observed task engagement as well as changes in a host of language and literacy skills. Engagement with tasks and activities in the classroom also partially mediates the association between self-regulation and changes in expressive vocabulary. Mediation through task engagement was not found for receptive language or early literacy skills. Practice or Policy: Findings suggest that the development and evaluation of clearly articulated preschool curricula designed to promote academic achievement by fostering self-regulation is an important direction for future research.