Abstract: In Kenya, the fundamental challenge facing learning of mathematics in secondary schools is how to enhance students’ conceptual understanding associated with the learning process. Based on this challenge, the study investigated the influence of using Problem Solving Approach on secondary school students’ mathematics achievement by school type. The purpose of this study was to determine whether the use of Problem Solving Approach had any influence on students’ mathematics achievement by school type. Students from one hundred and nine schools from Vihiga County formed the population of the study. Stratified random sampling was used to select twelve schools from the 109 schools. The population of the study was 1459 Form Three students selected from the twelve schools that participated in the study.