Background: Parent behaviours have a long-lasting impact on the health, education, and behaviour of the young people in their care. Group-based parenting interventions are a promising approach to improve parenting, as well as to prevent and reduce physical and emotional maltreatment of children. While a billion of adolescents live in low- and middle- income countries, few evaluations have examined parenting approaches for families with adolescents in these countries. Objectives: This study was nested within a randomised controlled trial of Sinovuyo Teen, a parenting programme for families with adolescents. The trial took place in rural South Africa in 2015-2016 with 552 families in 40 study clusters. Primary intervention outcomes included parenting and child maltreatment. This dissertation aims to: (1) describe the implementation (attendance, engagement, and fidelity) of the intervention delivered within the evaluation, (2) examine if participant characteristics affected attendance and engagement in the intervention, (3) examine if implementation characteristics affected programme results, and (4) examine if participant characteristics affected programme results. Methods: Programme implementation was assessed through observations of all programme group sessions and the records of the implementing organisation. The analyses also draw on participant self-report data from three time-points (baseline, immediate post-test, and follow-up). The data were analysed using a series of correlation and multilevel regression analyses, presented in three papers. Findings: Attendance levels in the intervention were somewhat lower than in previous similar studies, perhaps due to the role of home visits. Generally, more disadvantaged families participated at similar rates as families with more material and social resources. However, a number of factors affected attendance on individual and family levels, e.g. an overcrowded household, and at the community level, e.g. funeral and grant receipt days. Intervention fidelity was similar to the levels reported in high-income countries, thus suggesting that high implementation quality is feasible in a low-resource setting. There was no consistent impact of the variation in participation and implementation on participant outcomes. Baseline risks did not consistently affect variation in treatment effects, confirming recent findings that families at-risk can benefit from parenting support as much or more than less at-risk families.