The present study aimed to examine the affordances and constraints of small-group discussions in relation to student teachers' learning of science. By drawing on variation theory, this study focused explicitly on the student teachers themselves as the primary agents for providing opportunities for their own learning of science. The results show that student teachers were more likely to arrive at a common understanding of the object of learning when they adopted explorative talk, which included asking questions, testing ideas, and presenting differing views. Furthermore, explorative talk indicated a higher density in patterns of variation within and between relevant dimensions of variation. These results have implications for facilitating small-group discussions as part of student teachers learning process.