The aim of this study was to examine the mediating role of academic task engagement in the relations among family functioning, classroom contexts, and positive development among secondary school students in Bahir Dar, Ethiopia. To achieve this aim, correlational research design was employed. The target population comprised 16,725 students enrolled in 21 public secondary schools during the 2024/2025 academic year. A multistage clusture sampling technique was implemented, involving the random selection of schools and sections. The final valid sample consisted of 483 participants. Data were collected using validated self-report instruments assessing family functioning, student–teacher relationships, academic task value, academic task engagement, and positive development. Data analysis was conducted using descriptive statistics, latent correlation, and structural equation modeling with the Statistical Package for the Social Sciences (SPSS version 27) and Analysis of Moment Structures (AMOS version 23). The findings indicated that family functioning significantly predicted positive development both directly and indirectly. Student–teacher relationships and academic task value significantly predicted cognitive, behavioral, and affective engagement, which in turn predicted positive development, thereby confirming the partial mediating role of academic task engagement. The structural equation model demonstrated acceptable fit indices, suggesting that the proposed model adequately explained variations in students’ developmental outcomes. The study concludes that positive youth development is fostered through the combined influence of supportive family functioning, positive student–teacher relationships, meaningful academic task value, and active engagement in learning. Academic task engagement serves as a key developmental mechanism through which family and classroom resources are translated into positive developmental outcomes. To promote adolescents’ positive development, educational policies and practices should adopt an integrated ecological approach that simultaneously strengthens family functioning, enhances student–teacher relationships, and fosters meaningful academic task engagement with high task value, ensuring coherent collaboration between family and school contexts.