This study investigated the mediation mechanisms underlying the internal evolution of high-order thinking skills (HOTSs) among 132 seventh-grade students in China, focusing on the hierarchical relationships between specific HOTSs (S-HOTSs: evidence-based reasoning, model construction, systematic thinking and critical discussion skills) and complex HOTSs (C-HOTSs: critical-thinking and problem-solving skills). Using a longitudinal design with formative and summative assessments, the study employed single and chain mediation models to analyze HOTSs development during a 9-session biological science course on photosynthesis, respiration and the food chain. The results revealed that S-HOTS indirectly promote C–HOTS through sequential mediation pathways, with stronger effects from chain mediators compared to direct effects. Notably, model construction and systematic thinking skills emerged as pivotal mediators, bridging early-developing HOTSs and later-developing HOTSs. These findings highlighted the importance of stepwise instructional strategies aligned with hierarchical skill evolution, offering empirical insights for designing curricula that foster the development of HOTSs in science education. © 2025 Elsevier Ltd
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