Teachers teach more effectively when they are constantly updating their subject content knowledge and pedagogy as well as technology. This requires Continuous Professional Development (CPD) training programmes in order to cope with changing world in terms of nature of science, skills and technology. Therefore, the current study sought to demonstrate the improvements made by lower secondary school Mathematics, Physics, Chemistry, and Biology teachers following CPD training in content, pedagogy, using ICT tools (computers and projectors), and scripted lessons. The study's target population was 1100 Rwandan teachers in the 2021 cohort from eight districts. However, the analysis only included 652 mathematics and science teachers who took both pre-and post-tests. This study employed a quasi-experimental design. It collected quantitative data, through pre and post-test, to measure teachers' performance and conceptual grasp in mathematics or science courses. Kobo Toolbox was used to upload tests online and gather data, which was then exported to Microsoft Excel 2016, where each selected letter for each question was recorded. The acquired data were analyzed using Microsoft Excel 2016 and the Statistical Package for the Social Sciences (SPSS v.25). The findings revealed that overall teachers' performance improved, indicating that teacher misconceptions were addressed throughout training. Only a significant differences were found in the performance between male and female in both pre-and post-test in chemistry, among other subjects. It was also discovered that some concepts in respective courses need attention in the next CPD training programmes because teachers performed poorly on questions asked in these units per topic areas. It was recommended that the remedial training should be pursued for these teachers who did not perform well and further studies to investigate pedagogical changes as well as technological contribution in STEM education.