Science identity, encompassing perceptions of competence, interest, and recognition in science, alongside learning self-efficacy reflecting confidence to master science skills, are key drivers of outcomes. However, developmental patterns likely vary across contexts. Participants were 512 Chinese students spanning grades 1-3 who completed the Science Identity Scale and Science Learning Self-Efficacy Scale, with physics, chemistry, and biology achievement scores gathered. A Partial Least Squares Structural Equation Model assessed relationships. Results substantiated psychometrics for motivational measures. The model indirectly predicting achievement via first-order discipline-specific paths explained more variance than direct second-order effects. Effects significantly varied across groups stratified by grade and region. Interest and conceptual knowledge drove physics and chemistry success, while higher-order skills enhanced biology achievement overall. However, relationships differed within subgroups, suggesting personalized motivational support needs--self-belief/competence foundations for struggling learners, conceptual development for those with high prior achievement, and intrinsic enrichment for disinterested students. Results detail complex motivational profiles underlying science achievement requiring tailored identity safety and self-efficacy scaffolding alongside conceptual and skill-building for excellence across scientific disciplines. Motivational support systems may spur more equitable and optimal science outcomes among diverse adolescent learners.