School-based Professional Development and its influence on Education Managers' Service Delivery in Public Secondary Schools in Gatundu North, Kiambu County, Kenya

School-based professional development has been implemented as part of Kenya's decentralized capacity development programme. However, there is limited empirical evidence on its actual implementation, adequacy, and effect on education managers' service delivery at the sub-county level. Existing studies have focused primarily on teachers rather than education managers themselves. Thus, this article was guided by a research question: To what extent does school-based professional development influence education managers' service delivery in public secondary schools in Gatundu North, Kiambu County, Kenya? The study was grounded in the Human Capital Theory (HCT) and the Systematic and Blended Theory for Learning and Training. Using a convergent mixed method design combining both qualitative and quantitative methods concurrently, the target population comprised 339 respondents: 37 school principals, 37 chairpersons of Boards of Management (BOMs), six officers in the Sub-County Education Office, and 259 Heads of Departments (HODs). A multi-level sampling approach was applied, generating the sample through both probability and non-probability (purposive) sampling techniques. Schools were stratified by status. Data were collected using questionnaires, interview guides, and document analysis guides. Quantitative data were analysed using descriptive statistics, including frequencies, percentages and means while qualitative data from open-ended items, interviews, and document analysis were analysed thematically. The study found that school-based professional development positively influences education managers' service delivery (principals/BOMs composite mean=3.99, HoDs=3.65). This is particularly in fostering collaborative leadership and mentoring capacity. However, the persistent gap in classroom observation skills (3.68 vs. 3.34) and weak follow-up support constrain sustained practice improvement. Qualitative findings showed that while sessions build practical skills, follow-up support after training remains weak. The study recommends that the Ministry of Education should develop a national policy mandating systematic follow-up and reinforcement mechanisms for school-based professional development programs. Keywords: Decentralized Capacity Development; Public Secondary Schools; School-Based Professional Development; School Managers; Service Delivery