Verbs of knowing and other epistemological expressions were examined in transcripts of spontaneous conflict episodes in K-4th-grade classrooms. In 4,673 utterances there were 833 instances of epistemological expressions, with the proportion increasing with age and highest in teacher utterances. About one third of the children's epistemological expressions concerned certainty, contrasting knowledge with belief. These utterances were used strategically to regulate discourse, and they functioned differently in the conflict talk of children as compared to teachers. Children used expressions of uncertainty to soften challenges, whereas teachers used the same expressions to make indirect threats and commands. Besides certainty, epistemological expressions concerned accuracy, perception, meaning, veracity, and cognitive processes. Older children were more likely to talk about cognitive processes and veracity, and discussions about truth versus falsehood became more sophisticated in the oldest age group. Findings are discussed in light of what they reveal about the negotiation of meaning in everyday interactions and the development in context of a culturally shared, commonsense epistemology.