We study how teachers' rule violations in grading affect students' ethical behavior. Using administrative data from high-stakes exams, combining teacher-assigned internal scores with externally graded national exam scores, we track teacher grading violations and subsequent student cheating. We explore three potential mechanisms: imitation (learning that rules can be broken), positive reciprocity (responding favorably to favorable treatment), and negative reciprocity (retaliating against unfavorable treatment). Exploiting within-student variation in exposure to different teachers, we find students are significantly more likely to cheat when teachers break the rules to their detriment (systematically undergrading), consistent with both imitation and negative reciprocity. However, when teachers systematically overgrade, responses vary by community structure. In heterogeneous communities, overgrading increases student cheating, suggesting imitation dominates. In homogeneous communities, students respond by cheating less, consistent with positive reciprocity dominating. This pattern holds across multiple homogeneity measures, including surname concentration and residential clustering. Survey measures of mutual respect and support between students and teachers confirm this pattern.