This study documents gaps in kindergarten and first-grade science achievement by family income and explores the degree to which such gaps can be accounted for by student race/ethnicity, out-of-school activities, parental education, and school fixed effects. In doing so, it expands on prior research that documents disparate rates of science achievement by income in upper elementary and high school. The study uses nationally representative data from the Early Childhood Longitudinal Study of 2011. Findings suggest a science achievement gap of approximately 1 standard deviation between students from families near the 90th percentile of income and those from families near the 10th percentile of income. Race/ethnicity, out-of-school activities, parental education, and school fixed effects explain approximately one third of this gap each. The results suggest the need to focus on both in-school and out-of-school factors as part of a concerted effort to improve equity in science education.