Efforts to understand growth and disparities in science achievement have mainly been focused on the middle and high school grades in studies of K – 12 science education, leaving a gap in the research about the early elementary years. This study used a nationally-representative sample of students in Grades K – 2 to examine science achievement and growth trajectories of students by gender and race/ethnicity. Using multilevel growth modeling, differences in science achievement at Grade 2 and in rate of growth were detected for several student groups. Socioeconomic status, prior reading and math achievement, and student home language status were also significant predictors of science achievement. Growth effect size estimates were calculated by student group and showed substantial year-to-year growth in science achievement in the early elementary grades, with a slight decrease in effect size across years. In order to strengthen current efforts to increase student engagement and participation in science and STEM-related career and college pathways, especially for historically underrepresented groups, policymakers should shift focus to better understand promising practices that best support all students in science from the onset of their K – 12 educational experience.