The purpose of this study was to establish: (1) that Head Start children's emergent literacy knowledge would benefit from developmentally appropriate and child-centered intervention; (2) that children's emotional expression and regulatory behaviors are important predictors of interindividual differences in within-individual change in emergent literacy knowledge; (3) that warm and supportive navigation through a childcentered intervention would positively affect a child's perceived-self competence; and (4) that regular (i.e., daily) contextual assessment of emergent literacy is predictive of less frequent and more decontextualized assessments of emergent literacy. Children were randomly assigned to either an enriched literacy intervention group or to an attention control group. Group differences favoring the enriched literacy intervention group were found on emergent literacy and perceived-self competence measures. Random effects models indicated significant within-individual variation in initial status and change in both emergent literacy and perceived-self competence. Group membership, contextual assessment, regulatory behaviors, and emotional display significantly predicted individual differences in initial status and change. Preschoolers therefore respond to and learn from age-appropriate literacy-targeted instruction; behavioral and emotional indices are important indicators of individual change in literacy ability; and successful and enjoyable experiences during age-appropriate activities can impact children's perceivedself competence. Finally, regular and contextually relevant assessment can be an important tool used to monitor individual progress in young children's literacy abilities.