Effective curriculum supervision by head teachers is necessary for schools to offer quality education to learners. Learners’ assessment is one of the key areas of curriculum supervision. Thus head teachers should possess requisite knowledge, skills and attitude in supervision of learners’ assessment. In Bungoma West Sub-County low academic achievement was an issue in most public primary schools. In Kenya Certificate of Primary Education (KCPE) examination, the Sub-County’s mean scores for the year 2012 to 2014 were below average with performance indices of 237.22, 239.63 and 232.30 respectively out of possible 500 marks. This was attributed to various factors, with inefficiency in learners’ assessment often mentioned by stakeholders in the Sub-County as one of the factors. In-Service Education and Training (INSET) courses for primary school head teachers had previously been organized based on the whims of course organizers and not actual curriculum supervision needs of head teachers. The purpose of the study was to assess learners’ assessment supervision training needs of public primary school head teachers in Bungoma West Sub-County. Specific objectives were to determine the discrepancies between the ideal and actual learners’ assessment supervision knowledge, skills and attitudes of the head teachers. The study used descriptive survey research design. A conceptual framework comparing the ideal and actual outcome was used to guide the study. The study population was 81 primary school head teachers, 1 Sub-County Director of Education (SCDE) and 1 Teachers Service Commission Sub-County Director (TSC SCD). The research instruments comprised of head teachers questionnaire, interview schedule and document analysis guide. To ascertain reliability of the instruments, a pilot study was carried out involving 10% of the study population. Curriculum studies experts at Bomet University College were consulted to ascertain content validity. Test re-test method was used to determine an acceptable reliability Pearson coefficient of 0.9. Quantitative data was analyzed by descriptive statistics of frequencies, percentages and means. Qualitative data was grouped based on objectives and analyzed based on emerging themes. The study found very low discrepancy between ideal and actual learners’ assessment supervision knowledge and skills of head teachers (m=4.02). The study equally observed very low discrepancy in the attitude of head teachers towards learner’s assessment supervision (m=3.75). The study concluded that head teachers had training needs with regard to learners’ assessment. Based on the findings of the study, it was recommended that INSET courses for primary school head teachers should focus on participants’ knowledge, skills and attitudes in learners’ assessment supervision with specific emphasis on construction of various types of test items and mechanisms for monitoring quality of both internally and externally designed evaluation tests. The study is significant to the Ministry of Education and Teachers Service Commission Sub-County officials in the organization of INSET courses for head teachers. The study findings further contribute significantly to the knowledge in the field of teacher education and training.