This study examined the effectiveness of inquiry-based and lecture-based instructional approaches on the academic performance of Grade 11 Humanities and Social Sciences (HUMSS) students in Philippine Politics and Governance at Saint Columban College, Pagadian City. Grounded in Constructivist Learning Theory and the principle of scaffolding, the research aimed to determine the academic performance of students under both teaching approaches and identify whether a significant difference existed between them. A quantitative quasi-experimental design using a one-shot posttest two-group approach was employed. Twenty-four Grade 11 HUMSS students participated in the study. Data were collected through researcher-made posttests administered after the implementation of both instructional approaches. Descriptive statistics and a paired-samples t-test were used to analyze the data. Findings revealed that students exposed to the inquiry-based approach achieved a Mean Percentage Score (MPS) of 86.70%, interpreted as “Closely Approximating Mastery,” while those taught through the lecture-based approach obtained an MPS of 77.90%, interpreted as “Moving Towards Mastery.” Statistical analysis showed a significant difference between the two approaches (p = 0.033), indicating that inquiry-based instruction was more effective in improving students’ academic performance. The results suggest that inquiry-based learning promotes deeper understanding, critical thinking, and active participation among learners. The study recommends integrating inquiry-based strategies into Philippine Politics and Governance instruction while enhancing lecture-based teaching through interactive and student-centered activities.