Teachers are the cornerstone of a vibrant and sound education system, and their competencies, work ethic, and motivation are key in guaranteeing quality learner outcomes and the realisation of the national goals of education. Application of teacher interpersonal, supervisory competencies (TISC) during instruction is deemed to significantly impact student's academic performance, but this has not been so in Hoima District Government-aided secondary schools in Uganda. This is despite continued teacher instructional supervision, various legal provisions in place and government financing. The study assessed the relationship between Teachers' interpersonal and supervisory competencies and students' academic performance, to make recommendations to improve the situation. Self-efficacy and Self-determination theories premised the study of 149 respondents using a post-positivism paradigm, mixed-methods approach, where purposive and simple random sampling techniques were used in selecting sample size. Data was collected using a questionnaire, interview schedule and document analysis. Findings indicated a positive significant Pearson correlation coefficient (r (142) = 0.712, P<0.01) and inadequate teacher practising of a number of interpersonal competencies. Recommendations were: District Administration, Head teachers, School Boards, and parents should apply multifaceted approaches towards teachers encompassing professional development workshops and training sessions to develop their interpersonal and supervisory skills, increase their awareness on various social issues, and enhance their creativity and inventiveness in the supervision of student learning. This is in addition to developing supportive policies and practices regarding teaching resources and welfare. Additionally, teachers should maintain a collaborative relationship with parents/guardians and colleagues to develop and practice supportive, integrative, individualised attention to students while promoting collaborative networks with colleagues. The study further proposes that similar studies be carried out in other Government-aided secondary schools and private ones in Uganda