This study investigated the influence of headteachers' managerial strategies on primary teachers' performance in the implementation of Competency-Based Curriculum (CBC) in Kisumu Central Sub-County, Kenya. The objectives were to find out whether headteachers' supervisory strategies influence teachers' performance in the CBC and to establish how headteachers' parental engagement strategies influence teachers' performance in CBC implementation in primary schools in Kisumu Central Sub-County. The research was anchored on managerial role classification theory. A convergent, parallel, mixed-methods design was adopted. The target was public primary schools, headteachers, teachers, and the Quality Assurance and Standards Officer (QASO). Purposive sampling was adopted to include all 20 public primary schools, 20 headteachers, and one QASO in Kisumu Central Sub-County. Simple random sampling was used to select 304 out of the 440 teachers in the Sub-County. A questionnaire was adopted to get data from teachers. The collection of data from headteachers and the QASO was done through interview guides. The quantitative research instrument was validated by consulting the research experts, and the qualitative instrument was validated using the member checking technique. The reliability of the instruments was calculated through Cronbach's alpha, and a score of 0.789 was attained, which was considered reliable. Quantitative data was analyzed using the Statistical Package for the Social Sciences (SPSS) version 25, which was presented in percentages, frequencies, tables, graphs, and charts. Qualitative data was analyzed into themes and reported in narratives and direct quotations. The study found that head teachers do not effectively supervise teachers in the implementation of the Competency-Based Curriculum (CBC) in Kisumu Central