Mustapha, M.L.AMuhammed, S.AAlwajud-Adewusi, M.B.2018-12-032018-12-032016-030748-4710http://hdl.handle.net/123456789/1313Bullying behavior is a deliberate, unprovoked, aggressive behavior displayed repeatedly with the aim of harming or hurting others. It is characterized with imbalance of power (physical/psychological). This study investigated the effectiveness of Rational-Emotive Behaviour Therapy (REBT) in the reduction of in-school adolescents bullying behavior REBT is a theory based on the assumption that human beings are born with the ability of rational thinking and constructive behavior. The theory attributes bullying behavior to the irrational aspects of in-school adolescents belief system formed in childhood. The research design adopted in the study is quasl experimental in nature using 2x2x2 factorial design. It is made up of two(2) row groups (one experimental and one control) and two column groups (age and gender). Instrument used in purposively selecting the participant in the study was Bullying Identification Questionnaire (BIQ). Perpetrators of bullying behavior (i.e bullies only) were identified and participated in the study. REBT treatment procedure packages were administered to participants in the treatment. It was revealed that REBT produced administered to participants in the treatment group. It was revealed that REBT produced significant reduction in the bullying behavior of in-school adolescents, mean difference was observed in the pre and post-test scores of participants in the treatment group. ANCOVA was used to test for significant reduction of bullying behaviour yielding F=85.8, df (1, 47); gender and age had moderating effects on the reduction of bullying behavior of in-school adolescents F (df=1, 47)=34.2; F (df=1, 47)=51.9, p<0.05 respectively. It is recommended that REBT be used in the treatment of bullying behavior of secondary schools students.enBullying behaviorIn-school adolescentsRational-emotive behaviour therapy.Article