The study was conducted in the southern part of Mwanza region, from February to June 2015. The study area included public secondary schools from Kwimba district; district secondary education offices and Zonal inspectorate office. The study involved; Human capital theory, two factor theory; Lesson Study and Differentiated Supervision Model. Specifically, the study assessed external school inspecting strategies used by external school inspectors on improving teachers’ teaching, external school inspectors’ services delivery and curriculum implementation, challenges surrounding the whole task of inspecting schools, and means of arresting external school inspectors’ knowledge, skills and other conditions. The study categorized schools into two groups according to the design used, those were inspected many times felled into ‘control group’ and those received less inspections relied on ‘treatment group’. Again, the study used mixed research approach, where Non-experimental design specifically static group comparison was used. The study involved 192 respondents, questionnaires; semi-structured interview and reviewing written documents. Field data were analyzed through SPSS, where questionnaires’ findings were tested through T-test, Chi- square and ANOVA; and qualitative data were analyzed through descriptive way or written words. The findings showed that, somehow schools received more inspections benefited than those received fewer inspections, but wonderful enough, schools’ performance was the same in both groups. The study concluded that; the government provided poor support to inspectorate department, strategies used by inspectors were poor, and curriculum implementation was poor in schools. Recommendations, government should provide adequate support to inspectors, MoEVT should establish appropriate Models of inspection, open inspectorate offices to district, and inspectors to act as facilitator. The study provided further investigation about the contribution of school inspectors on students’ academic performance in public and private secondary schools, also the impact of Models of supervision on improving teachers’ teaching.