Weapon violence in schools is a pressing concern with serious consequences. In this study, we propose and evaluate a theoretical framework of school-based weapon violence comprised of contributors, triggers, and motivation leading to weapon behaviors, taking into account weapon type, origin, and availability. This framework provides a foundation to investigate the multifaceted nature of weapon violence in schools. Specifically, we examine the weapon violence experiences of 417 U.S. teachers based on their reports of their most upsetting experiences with violence in their schools from various aggressors (i.e., students, parents, colleagues). Qualitative open-ended survey data were coded in NVivo after achieving strong interrater reliability (Gwet’s agreement coefficient with first-order chance correction, AC1 = .97; κ = .80), and analyses were guided by the proposed theoretical framework. Results indicated that individual, school, peer, family, and community conditions contributed to situational triggers (teacher or other school-stakeholder actions), and aggressor motivation was typically instrumental or expressive. The type and origin of weapons also played a role in weapon behaviors of carrying, threats, and usage. Aggressors often used readily available objects (e.g., chair, pencil) as weapons against teachers in addition to traditional weapons (e.g., knives, guns). Findings suggest that weapon violence in schools requires a broader conceptualization beyond traditional weapons and violence between students. This study advances our understanding of pathways to weapon behaviors for prevention and intervention. Implications of findings for school-stakeholder training and policies are discussed.