The government of Kenya organizes staff development programmes in Public Primary Schools. However, a mean standard score of 248.52 at K.C.P .E. in Boro Division has been poor over the years. The purpose of this study was to explore the perceptions on the influence of staff development of teachers on learners' academic performance in K.C.P .E in Boro Division. The objectives of the study were to; find out perceptions on the influence of in-service courses for teachers on learners' academic performance, examine perceptions on the influence of further studies of teachers on learners' academic performance, examine perceptions on the influence of promotion of teachers to higher job groups on learners' academic performance and explore the influence of promotion of teachers to leadership positions on learners' academic performance. The study was guided by Capital Theory of school effectiveness and improvement by Hargreaves (2001). The study population was composed of 160 teachers, 39 head teachers and 39 deputy head teachers. The study sample constituted of 48 teachers, 12 head teachers and 12 deputy head teachers chosen through stratified random sampling. Descriptive survey research design was used in the study. Reliability of the instruments was determined by using test-retest method of Pearson product moment correlation coefficient r, and a coefficient of 0.7 was found reliable. Validity of the instruments was determined by two experts in the department of curriculum and education management. Questionnaires, In-depth interviews and Documentary analysis were used to collect data for the study. Quantitative data were analyzed by using Statistical Package for Social Sciences (SPSS) version 20.00 to produce descriptive statistics such as frequencies and percentages, while qualitative data were analyzed thematically. The study revealed that in-service courses of teachers enable them to learn new contents in respective areas, further studies allow teachers learn practical teaching approaches, promotion of teachers to higher job groups has not earned much in classwork since were based on further studies and not on performance and promotion of teachers to leadership enable them use stakeholders' input in school affairs. The study recommends that; in-service courses of teachers should be organized regularly by MOEST and T.S.C, teachers with higher qualifications should be used in mentoring new and practicing teachers and appointment to leadership should be based on teachers who have acquired skills in school administration. Studies on influence of pre-service teacher training on learners' academic performance should be done to augment findings of this study.