Introduction: Classroom incivility is low-level antisocial behavior that disrupts the overall learning environment. It is an important behavior to be studied in adolescence, given its associations with other antisocial behavior (e.g., bullying), negative impact on the learning environment, and predicting later aggressive behavior. The current study examined the developmental growth of classroom incivility in adolescence. Methods: We examined the growth of self-reported classroom incivility in a sample of Canadian grade 8-12 students (N[subscript T1] = 559; 54% boys; Mage = 14.9 years) with data from an on-going longitudinal study collected between Fall 2022 and Spring 2024. Results: Using growth curve modeling across ten timepoints of data collected over four waves of data collection, our findings suggested that the quadratic model fit our data best (compared to both a no-growth and a linear model). That is, our findings showed that classroom incivility increases in early adolescence, tapering off in the later grades (i.e., grade 11 and 12). Conclusion: Our results not only add important information about the developmental growth of adolescent classroom incivility to the current literature, but also provide insight that can be used by schools, suggesting that early adolescence might be a key developmental period for promoting civil behavior.