This study explored the mediating effect of student engagement on the relationship between deep approach to learning and academic achievement in Science among Grade 10 students from four private secondary schools in the Mati City Division, Davao Oriental. Descriptive and correlational methods, with mediation analysis, were employed to achieved the study objectives. A total of 117 Grade 10 students from the identified schools in the research locale were requested as research respondents. Adapted survey instruments were utilized to determine the extent of student engagement and level of deep approach to learning. On the other hand, a researcher-made summative test that underwent reliability test was utilized to determine students’ academic achievement in science. The results showed that students exhibited a high level of deep approach to learning and a very high academic achievement. Furthermore, student engagement was found to be highly extensive. Correlational analysis revealed significant relationships between the deep approach to learning and academic achievement in Science, between student engagement and academic achievement in Science, and between student engagement and deep approach to learning. Additionally, the study found that student engagement partially mediates the relationship between deep approach to learning and academic achievement of students in Science. These findings suggest that academic achievement can be considerably improved when students proactively adopt deep learning approaches. These strategies, combined with the facilitating role of teachers, prompt students to deepen their engagement across cognitive, emotional, and behavioral dimensions, thereby fostering a more holistic and effective learning experience.