While once forbidden in classrooms, laughter is increasingly encouraged as contributing to a positive learning environment. However, analyses of laughter in conversation show that laughter performs multiple social functions, some of which are not necessarily positive. Applying this lens, this study investigates the interactional functions of laughter in Israeli upper-primary classrooms. Using micro-­ethnographic, multimodal methods, we analyzed 27 laughter events drawn from 35 lessons taught by five teachers in four classrooms. We found that student laughter was for the most part treated as undesirable and occurred rarely. When it did occur, laughter primarily played a role in marking, maintaining, or negotiating symbolic and social classroom boundaries. Along with nonverbal cues, such as eye contact and body language, students' and teachers' laughter served multiple functions in relation to these boundaries, including emphasizing social boundaries, subverting teacher authority, bypassing norms, and responding to transgressions.