Background: Academic achievement in secondary education is shaped by a complex interplay of psychological, motivational, and environmental factors. Understanding these determinants is essential for designing evidence-based interventions to improve student outcomes.

Objective: This study examines the relative contributions of intrinsic motivation, academic self-efficacy, parental involvement, and teacher support to academic achievement (GPA) among secondary school students.

Method: A quantitative correlational research design was employed with 360 secondary school students selected through purposive sampling. Validated Likert-scale instruments measured intrinsic motivation, self-efficacy, academic engagement, parental involvement, and teacher support. Multiple linear regression was conducted using SPSS v29.

Key Results: The regression model explained 58% of the variance in GPA (R² = .58, F(5,354) = 97.83, p < .001). Self-efficacy (β = .34) and academic engagement (β = .32) were the strongest predictors. Intrinsic motivation (β = .25), teacher support (β = .15), and parental involvement (β = .10) also made significant independent contributions.