This study investigated the impact of Social Skills Training and Self-Efficacy Therapies on aggressive behaviours among Secondary School Students in Lagos State. To this end, a randomized two group pretest-posttest quasi-experimental research design was adopted as the blue print for the study, which requires the experimental groups to be treated with SSTT and SET. The sample consisted of 84 students in senior secondary school three (SSTT=42; SET=42) drawn through simple random sampling technique from two schools in Education Districts 2 in Lagos State. An adopted Measures of Aggression Checklist (MAC) was the instrument used for data collection. The test retest method was employed in establishing the reliability of the MAC, with two weeks interval between the first and second administrations. Data obtained were correlated using the Pearson’s Product Moment Correlation Coefficient statistic formula, which yielded a coefficient of r= 0.73. MAC was administered on participants in both experimental and control groups, after which the treatment was administered on the experimental groups for eight weeks followed by a post administration of MAC on participants in both groups. Data collected were analyzed using the Univariate Analysis of Variance at 0.05 level of significance. The result showed that there is no significant difference between the means of treatment effects for the different types of Aggressive behaviours among secondary school students in Lagos state who had Social Skill Training and their counterparts who had Self Efficacy Therapy with F (1, 70) = 0.475, p>.05, ηρ2 =.007. In general however, the Social Skills Training Therapy provided a higher reduction in aggressive behaviours than Self-Efficacy Therapy. It was therefore recommended that School Counsellors, Psychologists and other care givers should be properly equipped with psychological therapies, especially Social Skills Training so as to promote pro-social behaviours among secondary school students.