This study aimed to evaluate the effect of school supervision in improving learning effectiveness in public secondary schools in Ilala Municipality Dar es Salaam Region, Tanzania. The study employs mixed methods approach to collect data. Using an exploratory sequential design, the study involved 114 participant’s heads of school20, teachers, 380 students, 5 School Quality Assurance officers (QAOs), and 1 Ward School Officers. The study findings indicated that school supervision improved learning public effectiveness in secondary schools in the Ilala Municipality, Supervision provided direction, developed policies, analysed teaching-learning situations, identified problem areas and identified timely solutions, enhanced staff relationships, and improved group dynamics and resulted in overall positive school outcomes. Additionally, the study revealed that heads of school faced substantial issues, such as insufficient teaching/learning resources, shortages of funds, insufficient staffing, and excessive teacher turnover. Respondents suggested how the heads of school might strengthen their supervisory duties in their respective schools. To increase the quality of teaching and learning, school heads must involve teachers in the planning and execution of their supervisory tasks. There should also be a system that should involve stakeholders including such as parent’s online system to monitor pupils' academic achievement and also hold regular face-to-face meetings with key stakeholders.