<p>This study examines school-level quality enhancement practices in Ethiopian secondary schools and their influence on school effectiveness, using a mixed-methods approach. Data were collected from 32 randomly selected schools across four zones in Oromia Regional State, involving 388 participants, including teachers, principals, department heads, and PTSA members. Instruments included questionnaires, interviews, and document reviews. Quantitative data were analyzed using descriptive and inferential statistics, while qualitative data underwent reflexive thematic analysis. The results show that well-performing schools employ holistic quality enhancement strategies, optimizing resources, engaging communities, managing finances, planning strategically, fostering safe and supportive climates, enhancing professional development, maximizing instructional time, providing learning opportunities for students, and monitoring their progress, all anchored in committed leadership. These practices demonstrate a statistically significant correlation with academic achievement and explain differences in school effectiveness. Despite ongoing challenges such as infrastructure disparities, resource limitations, and academic performance concerns, schools can achieve meaningful improvement by adopting comprehensive quality enhancement strategies tailored to context, focused on strengthening inputs, and improving both school- and classroom-level processes.</p>