This study investigated the relationship between school practices and students' academic performance at the Uganda Advanced Certificate of Education (UACE) level in selected public secondary schools in Isingiro District, Uganda. A cross-sectional research design was employed, utilizing structured questionnaires to collect quantitative data from a sample of 327 respondents (teachers and students) selected through simple random sampling from a target population of 1,960 across five institutions. The data were analyzed to determine the correlation between effective school practices, such as lesson planning, classroom observation, and feedback support and students' academic performance. The results revealed strong, statistically significant positive correlations between all three practices and academic performance, with feedback support showing the strongest relationship (r = .818, p = .000), followed by lesson planning (r = .772, p = .000) and classroom observation (r = .688, p = .000). The null hypotheses were therefore rejected, confirming that the observed relationships were not due to chance. A multiple regression analysis indicated that these practices collectively explained 69.3% of the variance in academic performance (R² = .693). The study concluded that structured, consistent, and formative school practices are critical and meaningful determinants of academic success at UACE. It was recommended that school administrations implement targeted institutional policies focused on systematic lesson planning reviews, regular classroom observations with constructive feedback, and consistent academic progress monitoring to enhance instructional quality, foster teacher development, and ultimately improve student learning outcomes.