This exploratory study aimed to assess the strength of primary school students' (aged 11-12 years old) Science Self-Efficacy (SSE) beliefs, identify emanating sources, and investigate any gender-related differences. School SSE is defined here as perceived capacity to complete learning outcomes from the upper Irish primary science curriculum. The strengths and sources of participants' school SSE beliefs were assessed quantitatively (N = 260) using the Irish Science Self-Efficacy Children's Questionnaire (IS-SEC-Q). Twenty-five students were interviewed to further explore the origins of their SSE, and their perception of science in the classroom. Results indicated that students' self-efficacy to perform scientific skills was lower than their self-efficacy to answer questions. Mastery experience was found to be the strongest predictor of self-efficacy in science skills, corroborating findings from other educational contexts. However, students report that they seldom engage in hands-on science during school, suggesting that Irish classrooms still lack student-led investigations. Gender-related results are also highlighted. This work serves as the first report of students' school SSE beliefs in Ireland, expands upon existing literature surrounding the SSE beliefs of pre-adolescent students, and discusses implications for classroom practice.