This study compared the effects of two video-based lesson formats on undergraduate education majors' ability to interpret children's thinking with appropriate intellectual modesty. Participants in "guided video" and "unguided video" groups completed five web-based lessons on children's mathematical thinking. Each lesson entailed reading a short essay on a topic related to children's mathematical thinking (e.g., addition, equivalence) and then watching a short video of a child engaged in a relevant task and a clinical interview with an adult. In the guided video format, the video was segmented to produce frequent pausing, and the participant was prompted after each segment to answer questions about what the child did, was thinking, or would do next. After entering a written response for each prompt, participants were shown one or more plausible responses to the question before proceeding to the next video segment. In the unguided video format, the video was not segmented, and participants responded to questions only at the conclusion of the entire video. All participants, including a control group that received no lessons, completed pre-and post-tests with a video focusing on a different topic, namely the understanding of patterns. Participants in the guided video group significantly increased their use of interpretive statements and intellectually modest language (i.e., acknowledging ambiguity or uncertainty), while participants in the other two groups showed no significant improvement. These results suggest that regular, guided practice in the viewing of video might be useful for helping teachers make more thoughtful and modest interpretations of their students' thinking, which may in turn improve teaching.