Despite the government strengthening capacities of education managers, inducting subject teachers and funding day secondary education, many secondary schools still perform poorly in KCSE. The purpose of this study was to investigate the influence of supervision of instructional practices on teaching and learning in sub-county secondary schools in Bungoma County. The study adopted a mixed methods approach and a descriptive survey design. The study was based on Glatthorn’s theory of differentiated supervision which advocates for use of different supervision approaches for different circumstances. Using purposive and simple random sampling techniques, a sample size of 44 principals, 369 class teachers and 369 class prefects was selected to participate in this study, giving a sample size of 782 respondents Data was collected by using questionnaire and interview.