Management, administrative and leadership competence is critical for the educational goals of primary education to be realized. Primary school head teachers are faced with enormous changing managerial environments which has sometimes rendered them ineffective in their widening roles. Provision of targeted in-service training, therefore, has never been crucial. This study investigated the managerial skills that primary school head teachers in Marakwet West Sub-county required in-service training before enrolling for the KEMI Diploma in Educational Management Course. Descriptive survey research design was used. 38 head teachers selected using stratified random sampling from 57 schools whose head teachers undertook the KEMI Diploma in Education Management, 42 teachers randomly sampled and 13 chairpersons of the Board of Management purposively sampled from the same schools formed the sample. Questionnaires and interview schedule were used to collect data. The data collected was summarized, analyzed and presented using descriptive statistics such as mean, and standard deviation and inferential statistics such as paired sample T-test and correlation. The analysis was done using Microsoft Excel and Statistical Package for Social Sciences (SPSS) version 19.0. The data was summarized and presented using frequency tables, graphs and percentages. The findings of the study indicated that there was a significant improvement in leadership, administrative and managerial competence of primary school head teachers after undertaking the KEMI diploma in educational management. Head teachers were motivated by the need to upgrade their skills, salary increment and promotion in job grade. The KEMI diploma was however inadequate in advancing head teacher skill in ICT, Infusion of Emerging Issues and Financial management apart from the challenges associated with open and distance learning programmes. The study recommended for the job evaluation of head teachers to take an audit of skill requirements, continuous short term refresher courses in areas studied, decentralization of training and recognition of the academic attainment by head teachers through promotion and salary increment to motivate teachers pursue useful professional development programmes. The study identified gaps between the course content and the actual management skills required by the school managers, this include ICT skills and book keeping in financial management. The study further recommended policy review on the selection, promotion and deployment of Primary school head teachers by the TSC.