Research Findings: To test children's use of testimony of others, 3-9 years (N = 227) made judgments about a potential peer transgression in which the intentions of the protagonist were ambiguous, after hearing two different forms of testimony. The 2 forms of testimony were (a) opposing "opinion-based" testimony from an adult authority versus a peer consensus group and (b) "knowledge-based" testimony (eyewitness testimony) that was counter to the participants' initial judgments. Findings revealed that when testimony was presented in an opinion-based format, children were likely to side with the opinion that reflected their own interpretation of the peer encounter, regardless of whether the opinion came from a peer consensus or an adult authority. However, when knowledge-based testimony was introduced in support of the opposite of children's initial interpretation of the ambiguous peer encounter, children most often changed their initial judgment to align with the new testimony. That is, children used knowledge-based testimony but not opinion-based testimony to evaluate a potential transgression. Practice or Policy: These findings demonstrate that the way in which testimony is delivered to children has a direct influence on their decision making about peer interactions and has relevance for teacher-student discourse in the classroom.