Purpose: Previous research on pedagogical reforms has seldom looked at how reform may contribute to aggression in school organizations. The purpose of this paper is to hypothesize that teachers' disengagement from school mediates the tendency for teachers to manifest aggression when they are implementing pedagogical reform in school. Behind this hypothesis is the assumption that people are bound to encounter obstacles when implementing changes, and the resultant frustration can easily grow into feelings of disengagement and aggression which block the changes. Design/methodology/approach: In total, 845 teachers in 30 secondary schools in Hong Kong were surveyed and path analysis employed to look at how constraint in an organization and feeling of disengagement within the school hampers the successful implementation of reform towards constructivist pedagogy. Findings: Results of the study suggest that feelings of disengagement amplify the negative impact of instructional change and cause aggressive impulses within the school to intensify, but support from school can significantly reduce the feelings of disengagement and constraint experienced by teachers. Findings of the study contribute to a deeper understanding of the dynamics of change and its impacts on school organizations. Originality/value: Although some studies have looked at workplace aggression in a school setting, there is no work being done to look at how mandated school reform contributes to workplace aggression. (Contains 3 tables and 2 figures.)