Abstract: Despite policy efforts to improve access to secondary education, student performance and overall school efficiency in public secondary schools in Nyandarua County remain below expectations. This study investigated the effective implementation of 100% transition policy on school efficiency in public secondary schools in Nyandarua County, Kenya. It was guided by one research question: How does the implementation of 100% transition policy on access to public secondary schools’ influence school efficiency in Nyandarua County? Human capital theory was adopted. This was a mixed methods study that applied convergent parallel design. It targeted 180 public secondary,180 principals as well as 31,065 form three and four students. The study also targeted one County Director of Education. The study sampled 414 respondents. Questionnaires and interview guides were used to collect data from participants. Validity and reliability of the research instruments were tested. Verbatim and thematic approach analysis was done for qualitative data while quantitative data analysis was done by use of descriptive statistics with the help of SPSS version 26 software. The findings were that 100% transition policy has increased student enrolment in public secondary schools in Nyandarua County, leading to overcrowded classrooms and inadequate learning spaces. This strain on infrastructure has negatively affected teaching effectiveness, student engagement, and the overall quality of learning. Improvised learning areas and overburdened facilities, particularly laboratories, highlight the mismatch between increased access and available resources. 

Keywords: Implementation, 100% Transition Policy, Efficiency, Class Size, Public Secondary School