Kenya has experienced a gradual transition from a content-focused educational framework to a competency-based curriculum. However, transitioning to Competency-Based Curriculum has faced many challenges, particularly at the school level. This researchwascarried out to determine how school-based factors influence the implementation of Competency Based Curriculum in junior schools. Specifically, the study evaluated the influence of teachers' professional development, instructional materials, and school physical resources, on implementing the Competency Based Curriculum in junior schools in North Imenti Sub-County, Meru County. The research was guided by Adult Learning Theory, Cognitive Load Theory, and Ecological System Theory. The study used a descriptive survey design. The targeted schools for this research were 26 junior schools in North Imenti. The respondents were 2 sub-county education directors, 26 head teachers, and 70 junior school teachers. The sample size was 31. The data was collected using Questionnaires, interview schedules, and observation checklists. The collected data was coded and entered into Excel, where Quantitative data was analyzed using descriptive analysis. The findings were presented in tables and charts. Qualitative data collected from interviews were analyzed using thematic content analysis, and framework analysis was presented in narrative form. From the findings of this study, 71% of respondent revealed that teachers’ professional development influences implementation of CBC to a Great Extent while 29%indicatedaninfluence of Very Great extent. On school physical infrastructure, 70%of respondents indicated that classrooms very greatly influenced the implementation of CBC, followed by science laboratories with 63%, then playgrounds with 53%, ICT infrastructure with50%, while agricultural plots and workshop with 50% respectively. On instructional materials, course books were rated the most influential material in the implementation of CBCwith85%, followed by teachers’ guide with 70%, then digital tools with 60%and finally teaching aids with 45%. The study established that teachers to be trained more on subject-specific methodologies, pedagogy, and learner assessment under CBC. Challenges identified included irregular teacher training, limited follow-up support, especially in remote areas, and inadequate facilities such as libraries and workshops. The study concluded that sustained professional development, adequate learning resources, and improved infrastructure are essential for effective CBC implementation.