Out-of-field teaching is viewed as inferior to subject-specific instruction, but its impact on student outcomes varies depending on the criteria used for evaluation. The present study investigated the consequences of out-of-field teaching in science on different student outcomes on an international scale. Analyses were based on the sixth cycle of PISA data, using a subsample of N = 128,438 students (51% girls) and N = 27,819 teachers (44% women) from 4,037 schools in 18 countries. Results show that higher specialised science teachers rates in schools were linked to improved scientific literacy and students enjoyment. Science teachers with specialised science training in a school were associated with higher science competencies in students, while the impact on the enjoyment of science was smaller. However, the share of specialised teachers was not associated with students' self-efficacy or perceived teaching practices. The findings suggest that specialised teachers are critical in positively influencing students' literacy and enjoyment. Moreover, it informs policymakers and school administrators about the need to prioritise hiring specialised science teachers to improve the overall quality of science education. Further research is needed to understand how specialised teachers affect student outcomes and to identify other factors impacting science literacy.