Abstract Conflicts between informal groups are common in adolescence, and can lead to much aggression, but have been much less studied than conflicts between stable groups such as gangs. Seeking to understand better their conflict dynamics, informal groups were identified with a peer‐nomination method applied to 121 adolescents from Bogotá, Colombia (12–16 years), and 23 semi‐structured interviews were conducted. Most conflicts escalated to verbal or physical aggression. Whether conflicts escalated or de‐escalated seemed to depend on beliefs legitimizing aggression, social identities, online (vs. face‐to‐face only) interactions, and on third parties interventions. Results provide insights for prevention of school violence.