Stronger metacognition, or awareness and regulation of thinking, is related to higher academic achievement. Most metacognition research has focused at the level of the individual learner. However, a few studies have shown that students working in small groups can stimulate metacognition in one another, leading to improved learning. Given the increased adoption of interactive group work in life science classrooms, there is a need to study the role of social metacognition, or the awareness and regulation of the thinking of others, in this context. Guided by the frameworks of social metacognition and evidence-based reasoning, we asked: (1) What metacognitive utterances (words, phrases, statements, or questions) do students use during small-group problem solving in an upper-division biology course? (2) Which metacognitive utterances are associated with small groups sharing higher-quality reasoning in an upper-division biology classroom? We used discourse analysis to examine transcripts from two groups of three students during breakout sessions. By coding for metacognition, we identified seven types of metacognitive utterances. By coding for reasoning, we uncovered four categories of metacognitive utterances associated with higher-quality reasoning. We offer suggestions for life science educators interested in promoting social metacognition during small-group problem solving.