The research study identified the prevalence of indiscipline among secondary school students. It examined the effects of indiscipline among students and identified principal's attitude to indiscipline in secondary schools in Ondo State. Descriptive research design was employed. Questionnaire was administered on 500 Senior Secondary Students to know the prevalence, effects and principals' attitude to indiscipline in Secondary Schools. The instrument was validated by experts in tests and measurement, and a reliability coefficient of 0.84 was established using Cronbach Alpha at the 0.05 level of significance. The study found out that there is high prevalence of indiscipline among secondary schools students in Ondo State which has significantly affected students' interest in schooling and overall students' academic performance in school. It also observed that most school principals put-up lackadaisical attitude to indiscipline in their schools while some even aid and abet through their actions and behaviour. The study concluded that unbiased appointment of capable and effective principals, and effective monitoring of schools will ensure discipline which will boost the quality of teaching and learning for the attainment of the set goals in secondary schools.