Science subjects are the backbone of the scientific and technological advancements in the world. Achievement in science subjects in secondary schools in Kenya has been below average. The low achievement in the national examinations has been attributed mainly to teacher centered teaching approaches used by teachers. In an attempt to address the low achievement in Physics, the Strengthening of Mathematics and Science in Secondary Education (SMASSE) teaching program was introduced through In-service Education and Training INSET) in the whole of Kenya in 2004.Therefore, this study was an attempt to fill this gap. The objectives of the study were; to find out whether SMASSE approach had impacted the achievement in physics and whether there was a gender difference in the achievement in Physics among secondary school students in Konoin sub-county. The study used expost-facto research design as well as a survey research design. Stratified and systematic sampling was employed to select schools for this study. The population was the KCSE candidates in Konoin Sub- County and the accessible populations were the 2000-2003 candidates before SMASSE was introduced and 2012-2015 KCSE candidates immediately after. There was a total of 5017 candidates in this target class in 24 secondary schools in Konoin Sub-County in period 2000-03 and 5204 in the period 2012-15. The schools were in 3 categories, these were extra-County, county, and sub-county schools and both stratified, systematic sampling and purposive sampling were used to select 12 schools with a total of 1013(685 boys and 328 girls) students for the period 2000-2003 and 1390 (1009 boys and 381 girls) in the same 12 schools for the period 2012-2015 took part in this study. The research instruments used for the study were a Document analysis tools. Descriptive and inferential statistics were used in the analysis of data, a one-way ANOVA was used as inferential statistic to test the null hypothesis. All statistical tests were subjected to a test of significance at coefficient alpha (α) of 0.05. The study found out that there was no statistically significant difference between those students who were exposed to SMASSE and those who were not. The findings may inform decisions and action towards improving teaching and learning of Physics in Kenya. The study also may help to sensitize teachers, curriculum planners, policy makers and other education stake holders as far as SMASSE program is concerned on the areas that require improvement.