This study examined the relationship between headteachers' leadership practices and students' discipline in secondary schools in Bushenyi-Ishaka Municipality, Uganda. Particularly, the study tested the relationship between headteachers' collaborative culture practice and students' discipline, the relationship between headteachers' distributed leadership practice and students' discipline, and the relationship between the headteachers' interpersonal relationships leadership practice and students' discipline. The cross-sectional design was adopted using the quantitative and qualitative approaches. Data were collected on a sample of 310 teachers using a questionnaire survey. The findings revealed that while the collaborative culture and interpersonal relationship had a positive and significant relationship with students' discipline, distributed leadership had a negative and insignificant one. Therefore, it was concluded that the collaborative culture leadership practice is imperative for promoting students' discipline in secondary schools, distributed leadership practice is not an essential practice for promoting students' discipline in secondary schools, and interpersonal relationship leadership practice is vital for the promotion of students' discipline in secondary schools. Therefore, it was recommended that headteachers should promote collaborative culture practice in schools to promote students' discipline, headteachers should not over-emphasise distributed leadership in implementing measures of promoting student discipline, and headteachers should prioritise enhancing interpersonal relationships in secondary schools to promote students' discipline.