Although 3-year-olds in the United States may attend prekindergarten prior to formal school entry in kindergarten, few investigations focus on the socioemotional foundations of classroom learning at age 3 and their relationship to later achievement. This study examined the relationship between age 3 readiness for group-based learning, modeled as the latent constructs, effortful control and social communication, and age 5 classroom adjustment and pre-academic outcomes. Data from the Early Head Start Research and Evaluation Project in the United States (n = 797) included observations, direct assessment, and examiner and teacher report. Children's effortful control predicted classroom adjustment and their social communication predicted pre-academic outcomes. Readiness for group-based learning provides a way to describe key constructs of early skill development and a framework to support children's classroom learning. Implications include promoting parents' and educators' capacities to support early developmental foundations for later adjustment and learning by fostering infants' and toddlers' effortful control and social communication. Efforts to support these skills simultaneously across diverse experiences in the home and classroom by focusing on children's individual needs may prove advantageous. (author abstract)