This research study focused on investigating the use of 5Es instructional model by physics teachers and how the model impacts the learning process of the basic concepts of electromagnetic waves in physics. In this study, six advanced-level physics teachers in four secondary schools within the Rwamagana district in Rwanda were purposively selected to participate. To collect data, 48 classroom observations were conducted, and data collected from classroom observation on the lesson delivery for all six teachers were analyzed through descriptive statistics. Before the training, the overall scores of observed lessons were low (M=2.07; SD=0.68 out of 5) corresponding to 40.1% across all the 11 statements of classroom observation tool used to assess secondary schools STEM teachers' ability to plan and conduct teaching based on 5Es instructional model. After the training on 5Es instructional model, a significant improvement for all teachers in lesson preparation and its delivery was achieved. The high mean scores, M=4.79 out of 5 scorerates (95%) with low standard deviation, SD=0.40 across all the 11 statements of similar classroom observation tool were obtained. The results after the training on the model indicated good performance for all teachers in terms of integrating exciting activities, discrepant events, relevant visualization guide, boosting learners' confidence to express their ideas in the teaching process, and using constructive scenarios that helped the learners to relate what they learned to real-life situations. Therefore, the use of the 5Es instructional model was found effective and recommended as a useful teaching approach for teachers.