Purpose: The success of schools fundamentally depends on teachers' willingness to go above and beyond the call of duty, namely, to exhibit organizational citizenship behaviors (OCBs). Attempts to understand the causes of OCB frequently focus on individual characteristics; only recently have researchers begun to direct their attention to more contextual variables. The present study continues this line of research and proposes an integrative model. This allows the authors to examine simultaneously the relative impact of individual characteristics (dispositional variables of positive affectivity, negative affectivity, and teacher attitude) to perceived superior support and an organizational characteristic (of organizational values of individualism versus collectivism) on OCB at school. Method: Data were collected from a survey of 104 teachers and their principals at eight elementary schools in northern Israel. Results: A mixed models analysis demonstrates that perceived supervisor support and collectivism were positively related to OCB, whereas a negative relation was found between negative affectivity and OCB; no relation was found between positive affectivity and OCB. However, when these variables were examined simultaneously, the organizational variable of collectivism proved the most effective predictor of OCB. Implications: The present results should serve to encourage OCB researchers to focus more attention on characteristics of organizational context as related to OCB. Schools are powerful suppliers of norms to their teachers, and exchange relationships that form within schools, as well as collective values, may partly determine the level of OCB in them. (Contains 1 figure and 5 tables.)