A large body of research has studied the role and potential of inquiry to increase the quality of teaching in science education. While much of this existing research is based on international large-scale assessment studies, we still lack a clear understanding of the factors that influence the quality of inquiry-based science teaching in actual classroom practices. In this paper, we operationalise teaching quality through an observation manual, and we drew on this manual to systematically analyse video data of instructional practices in 20 Norwegian science classrooms at the primary and lower-secondary school level (73 observed lessons and about 450 students). We identified varying quality in the individual inquiry phases and differences between primary and lower-secondary schools. We observed that primary-school students collected and documented data more systematically than lower-secondary students and that consolidations were slightly more emphasised and of higher quality at the lower-secondary than at the primary level. Moreover, our findings indicate that inquiry-based teaching gave students more freedom to make their own choices and increased the quality of student participation in the classroom. Based on our findings, we discuss how teachers can improve the quality of inquiry-based instruction and empower students in the classroom.