This study examined the usability of warnings by school heads to enhance teachers’ discipline in public secondary schools in Biharamulo District. The study was guided by Jeremy Bentham's Utilitarianism theory (1789). The study employed a convergent research design under mixed research methods. The target population was 1 District Secondary Education Officer, 1 TSC Assistant Secretary, 21 heads of schools, and 481 teachers. The study used stratified random and total population sampling techniques to determine the sample of 79 respondents. Interview guides and questionnaires were used to collect data. Face and content validity was ensured by two MWECAU research experts. Pilot testing was done in two public secondary schools. The reliability was estimated to Likert-items type using Cronbach alpha whereby r=0.784 for teachers' questionnaire. Triangulation and peer debriefing were used to ensure the reliability of the interview guide. Descriptive statistics were used to analyse quantitative data in frequencies, percentages and mean with the aid of SPSS version 22 and presented in tables. Qualitative data were analysed by developing quotes, codes, and themes, which were presented in direct quotations. The study found that heads of schools used warnings to a large extent to address teachers' indiscipline behaviours. Furthermore, the study revealed that, although some heads of schools avoided using written warnings to prevent conflicts, verbal and written warnings were still commonly used to maintain school discipline and good academic performance. The study concluded that warnings were effectively used to maintain teachers' discipline in public secondary schools. The study recommended that heads of schools should keep on using warnings to improve teacher discipline. However, the government, through the Teachers Service Commission (TSC), should educate heads of schools on the correct usage of warnings to prevent teachers from engaging in indiscipline behaviours and avoid conflicts among school administrators and teachers.