This study investigated (i) the effect of inquiry-oriented laboratory activities on preservice primary school teachers' (PPSTs) achievement in science process skills (SPS) and science teaching efficacy beliefs, and (ii) changes in groups' reflections of SPS in the laboratory reports as they engaged in the activities. There were 71 PPSTs enrolled in a science laboratory course. Of the 71 PPSTs, 61 who completed the Science Process Skills Test and Teachers' Sense of Efficacy Scale both at the beginning and at the end of the course constituted the sample for the former purpose of the study. On the other hand, 71 PPSTs formed groups to work on the laboratory activities and reports collaboratively, which resulted in a total of 17 groups that were involved in the study for the latter purpose. Findings indicated that PPSTs' achievement in SPS and reflections of SPS in the reports improved in the inquiry-oriented laboratory environment. Furthermore, experiencing the intervention contributed to PPSTs' science teaching efficacy beliefs for instructional strategies, student engagement, and classroom management. Implications for teacher education programs and recommendations for future research are presented.