The head teachers' role is to promote academic performance. It is therefore important that the performance of a school is appraised against the performance of the person who leads it. The purpose of the study was to investigate the instructional role of the head-teacher in academic achievement in Kenya Certificate of Secondary Education (KCSE) examinations in Vihiga district of Western province. The population of the study comprised 84 head-teachers and 1,280 teachers serving in the 84 secondary schools. Saturated sampling technique was used to select a sample from the high and average performing schools, while stratified random sampling technique was used to select a sample from the low performing schools. The sample comprised 7 high performing schools, 17 average performing schools and 20 low performing schools. All the 44 head-teachers of the selected schools formed part of the sample for the study together with 8 teachers from each school sampled randomly. Data was collected by use of questionnaires, in-depth interviews and document analysis guide. Data was analyzed by the use of descriptive statistics of frequencies and percentages. The findings of the study showed that head-teachers' instructional role included regular checking of teachers' professional records, regular class supervision, and management plan for carrying out curriculum goals. Therefore, since the role of the head-teacher is associated with high student achievement, the study recommends that head-teachers should enhance internal supervision of teachers. (Contains 3 tables and 2 figures.)