In recent years, inquiry-based science instruction has become widely advocated in science education standards in many countries and, hence, in teacher preparation programmes. Nevertheless, in practice, one finds a wide variety of science instructional approaches. In South Africa, as in many countries, there is also a great disparity in school demographic situations, which can also affect teaching practices. This study investigated the pedagogical orientations of in-service physical sciences teachers at a diversity of schools in South Africa. Assessment items in a Pedagogy of Science Teaching Test (POSTT) were used to identify teachers' science teaching orientations, and reasons for pedagogical choices were probed in interviews. The findings reveal remarkable differences between the orientations of teachers at disadvantaged township schools and teachers at more privileged suburban schools. We found that teachers at township schools have a strong "active direct" teaching orientation overall, involving direct exposition of the science followed by confirmatory practical work, while teachers at suburban schools exhibit a guided inquiry orientation, with concepts being developed via a guided exploration phase. The study identified contextual factors such as class size, availability of resources, teacher competence and confidence, time constraints, student ability, school culture and parents' expectations as influencing the methods adopted by teachers. In view of the recent imperative for inquiry-based learning in the new South African curriculum, this study affirms the context specificity of curriculum implementation (Bybee 1993) and suggests situational factors beyond the curriculum mandate that need to be addressed to achieve successful inquiry-based classroom instruction in science.