Scholars have contended that cyberbullying perpetration is a learned social behavior, and one way to show evidence for cyberbullying learning is to test the longitudinal reciprocal relationships between cyberbullying behavior and related cyberbullying-related cognitions (e.g., attitudes). A paucity of research has tested these learning tenets, and no research that we are aware of has examined the moderating role of sex. The current study used a two-wave longitudinal design with US youth. Participants completed measures of cyberbullying attitudes and perpetration. Results showed that early cyberbullying attitudes and behavior predicted later cyberbullying attitudes and behavior; however, and most importantly, sex moderated those relationships. Males had stronger longitudinal relationships than females. Results are interpreted regarding theory.