This research aimed to construct and validate the School Conflict Negotiation Effectiveness Questionnaire (SCNEQ). This objective is both based on the increasing relevance of the area of constructive conflict management in schools and also in the scarcity of instruments that try to measure these dimensions in the educational context. We used two samples of students from middle and high school in two urban public schools, one with 622 students and another with 505, the last one to confirm validation. The results of the samples show values of Cronbach’s alpha of .84 and .87, respectively. The data suggest the feasibility and validity of SCNEQ to assess the construct under study. We consider it relevant to continue the psychometric studies of the scale, so future research should address this topic in depth. Concerning the findings, results of the present study reveal that affective groups statistically differ in their self-reported conflict management styles.