Early childhood researchers from across the U.S. came together to form the Early Learning Network (ELN) in 2016 with the mission to identify policies and practices that narrow opportunity gaps and help children maintain early learning success. Early Learning Network teams share what they have learned--and what it means for early childhood education practice and policy--in a series of research briefs. The briefs summarize impact areas that have potential to positively contribute to young children's learning and development, including key takeaways and action steps for practice, policy and research. This brief focuses on the impact area of pre-K participation. The initial positive effects of pre-K on children's academic and social-emotional skills (pre-K boost) may diminish or disappear by the end of kindergarten. This pattern appears to be due to non-attenders quickly catching up to their peers, and not children's skills fading out over time. Findings suggest there are different levels of catch-up for different types of skills. Pre-K programs and the early elementary grades should prioritize instruction in both foundational skills (e.g., counting, letter recognition) and complex skills (e.g., vocabulary, self-regulation) to promote lasting pre-K gains, particularly for students who are marginalized.