This paper discusses the disciplinary practices employed by teachers on boys in coeducational secondary schools in Kenya based on a study on the effect of coeducation on the discipline and academic performance of boys. Data was collected through structured face-to-face interviews with six teachers in charge of discipline in six mixed boarding schools in Nakuru District. The findings revealed that the coeducational setting presented unique challenges to boys’ discipline. Moreover, boy-girl affairs, which abounded in such settings, resulted in poor academic performance for the boys. The boys were lacking in academic focus, indulged in petty theft and exam cheating and other related vices in order to win the admiration of girls in school. Further, disciplinary practices adopted by teachers in the schools were unfavourable to the boy child’s general well being and indeed were detrimental to boys’ academic performance. The negative effect of such practices manifested in the form of low self esteem, lack of confidence, embarrassment, humiliation and loss of interest in academic work. It was recommended that school administrators employ stringent measures to discourage unhealthy relationships among students in mixed schools and structured forms of punishment be employed to correct the behaviour of the boy child.