There are ongoing calls for research that identifies students' conceptions about geographical phenomena. In response, this study investigates junior secondary school students' (N = 95) conceptions about plate tectonics. Student response data was generated from semi-structured interviews-about-instances and a two-tiered multiple-choice test instrument developed and validated by the researchers. There were three main findings: (1) students held many alternative conceptions about plate tectonics, most of which have not been reported in previous research; (2) students' alternative conceptions most commonly concerned the formation of landforms at tectonic plate boundaries; and (3) students were particularly confused about the cause of subduction at an oceanic-continental convergent plate boundary. The findings of this study can assist geography teachers and researchers to develop innovative pedagogies that consider students' pre-instructional alternative conceptions and promote conceptual change learning.