The effectiveness of school systems and learners’ academic performance in Kenya relies heavily on head teachers’ instructional leadership practices and teachers’ work performance, raising the need for suitable instructional leadership practices to achieve the desired quality of education outlined in Vision 2030 and the fourth Sustainable Development Goal. However, recent reports highlight concerns about teachers’ work performance, especially regarding their classroom pedagogical knowledge, skills, and practices. The purpose of the study was to assess the influence of provision of professional development opportunities by the head teachers on teachers’ work performance in public primary schools in Nakuru County, Kenya. Hallinger and Murphy’s (1985) Model of Instructional Leadership and Campbell et al.’s (1993) Theory of Job Performance informed the study. The study employed a mixed methods approach with the convergent parallel design, collecting both quantitative and qualitative data from 466 respondents in 68 primary schools. The sample included 60 pupils, 329 teachers, 68 head teachers, and 9 Quality Assurance and Standards Officers (QASOs). Data were gathered through questionnaires, interviews, focus group discussions, and document analysis. Statistical analyses in SPSS version 25 included descriptive statistics, percentages, Spearman rank correlation, and regression analysis. The results show that the provision of professional development by head teachers had no significant influence on teachers’ work performance in public primary schools in Nakuru County.The study concluded that teachers’ work performance was critical for the overall school outcomes. The study recommends that head teachers should implement internal professional development programs, considering key procedures like identifying teachers’ training needs for instructional improvement, encouraging in-service training, providing guidance on performance gaps, organizing peer coaching, and promoting further studies for career advancement.