A person-centered approach was used to explore how preschool school readiness profiles predict Grade 3 academic performance among a large (N = 43,044) low-income, ethnically-diverse longitudinal sample of children. Study aims: (a) determine the number and type of preschoolers' school readiness profiles, (b) determine how profile membership relates to demographic characteristics, and (c) use the profiles to predict Grade 3 academic achievement. Six profiles were found: Pre-academic strength (PAS) strong school, average home behavior; PAS-average school, low home behavior; PAS-average school, strong home behavior; Pre-academic weakness (PAW) average school, low home behavior; PAW-low school, average home behavior; and Overall poor school readiness. Demographic characteristics were associated with profile membership, and profiles were differentially related to Grade 3 outcomes, after controlling for demographic factors. Results highlight the importance of starting school with strong social skills at school (vs. home) and the potential benefits of public school pre-K boosting children's social/emotional skills.