Purpose: The prevalence, risk factors and effects of work on school performance and health consequences of child labour among school children in a rapidly urbanising community in south west Nigeria was assessed. Methods: A descriptive cross-sectional study of 386 Junior Secondary School students was conducted. Questionnaires were used to obtain information on the students’ socio-demographic characteristics, history of child labour activities, and recent history of illness. The academic records of the students were also reviewed. Results: The prevalence of child labour was 72.5%, the median number of hours spent working per week was 18 hours (range 2- 56 hours). The main reason for working was to augment the family income (37.6%). Child labour was commoner among those: whose mothers were not educated; who had four to eight siblings, and who had a working sibling. Higher proportions of working children had repeated a class and had failed the previous term’s examinations. More of the working children reported being ill and injured in the previous term. Conclusion: Child labour is quite common in this area and is associated with negative academic and health outcomes. Multidisciplinary programmes targeted at reducing the practice should be developed.