Classroom observation is a critical tool for evaluating instructional strategies and their impact on student learning outcomes. This study investigates how implementing systematic problem-solving strategies affects teaching practices, classroom dynamics, and student engagement in Rwandan secondary school physics classrooms. A quasi-experimental design with non-equivalent control groups was adopted, involving 160 senior-five (Grade 11) physics students from four selected public schools--two from urban and two from rural districts. The experimental groups received structured training in systematic problem-solving strategies, while the control groups continued with conventional teaching methods. Data were collected using the Reformed Teaching Observation Protocol (RTOP) before and after the intervention. The findings reveal statistically significant improvements in teaching practices, classroom culture, and student engagement in the experimental groups compared to the control groups. Notably, procedural knowledge and communicative interactions showed the most substantial gains. A t-test analysis confirmed that the experimental groups outperformed the control groups across all RTOP themes (p < 0.01). These results underscore the potential of structured problem-solving approaches in enhancing physics education by fostering active learning and critical thinking. This study contributes to physics education reform by providing empirical evidence supporting structured problem-solving methodologies in competency-based curricula. It advocates for integrating student-centered teaching strategies to bridge gaps in problem-solving abilities among secondary school students.