This study investigates the relationship among student engagement, learning strategies, and academic achievement. Data were collected from 4,825 eighth-grade students in Guangzhou, China, using the Delaware Student Engagement Scale (DSES) and the Motivated Strategies for Learning Questionnaire (MSLQ). Structural Equation Modeling (SEM) with mediation analysis revealed that both student engagement and learning strategies positively predict academic achievement, with learning strategies fully mediating the effect of engagement on achievement. While higher engagement generally leads to greater use of learning strategies, students with high engagement but low strategy use perform significantly worse than those with lower engagement but more effective strategy use--supporting the concept that "ineffective methods lead to wasted effort." Findings show that cognitive engagement was the lowest among the engagement factors, while organizational strategy was the lowest among learning strategy dimensions. Female students exhibited more effective strategy use than their male counterparts. Practical implications suggest that educators focus on improving students' learning strategies, especially organizational skills, to enhance academic performance and address gender differences. However, due to the study's cultural context, the results may not be generalizable across all populations, underscoring the need for further research in diverse settings.