This study examined the science self-efficacy beliefs of students at the transition from elementary school (Grade 6) to middle school (Grade 7) and the transition from middle school (Grade 8) to high school (Grade 9). The purpose was to determine whether students' perceived competence is impacted at these important school transitions and if the effect is mediated by gender and ethnicity. Science self-efficacy was measured through a modified Self-Efficacy Questionnaire for Children, which was adapted to focus specifically on science self-efficacy. Multiple ordinary least squares regression was used to analyze the data. Two models were developed, one using ninth grade as the comparison group and the other using sixth grade as the comparison group. In each model, the independent variables (grade level, gender, and ethnicity) were regressed on the dependent variable, science self-efficacy. The most striking finding was the large and significant decline in science self-efficacy scores for ninth graders at the transition to high school. We also found that females and Hispanic students had lower scores across grades as compared to males and Caucasians. How these results relate to existing studies, and implications for practice and future research are discussed.