This book presents the findings of a study that was designed to investigate the relationship between peer group attitudes towards school, peer group activities and academic achievement of secondary school students in Nairobi urban area in Kenya. Adolescents peer group relationship has increasingly become a significant factor that influences their behaviors in Africa. This is because of the urbanisation processes that are increasingly segragating children from their parental monitoring. Most parents are busy in their work places leaving adolescents to opt for their peer group guidance and advice. Teachers, on the other hand, are overwhelmed by curriculum coverage, hence having less time to closely monitor the behaviors of teenagers and their peers. Thus, some of the peers influences may impact on learners academic achievement in one way or another. Therefore, the findings of this study are of significance in understanding the role played by peers in adolescents school achievement for a number of stakeholders in education including students, parents, teachers and policy makers.