CEFContemporary Education Frontiers3029-18793029-1860Bio-Byword Scientific Publishing Pty. Ltd.10.18063/CEF.v4i4.1894ArticleProject-Based Learning and Preschoolers’ Collaborative Problem Solving: A Sequential Explanatory Mixed-Methods Protocol Testing Srl Mediation and Scaffolding Moderationhttps://artdesignp.com/journal/CEF/4/4/10.18063/CEF.v4i4.1894HanBingqian,DouJiaping,LiXuelai2026442026-04-26Project-based learning (PBL) is widely promoted in early childhood education as a pedagogy that can cultivate cooperation and problem-solving through sustained inquiry and collaborative artifact construction. However, cooperation and problem solving are often assessed as parallel outcomes, leaving the coordinated process that links them underspecified. Derived from a doctoral dissertation on the coordinated development of preschool children’s cooperation and problem-solving ability, this manuscript presents a sequential explanatory mixed-methods protocol (QUAN → QUAL) that conceptualizes coordination as collaborative problem solving (CPS)—the integrated capacity to build shared understanding, coordinate actions, and organize participation toward a joint goal. Using a 12-week quasi-experimental pre-test/post-test design with a matched comparison group, the study tests whether structured PBL produces larger gains in CPS than regular instruction, whether gains are partially explained by improvements in observable self-regulated learning (SRL) routines, and whether teacher scaffolding quality and functional focus strengthen or weaken these pathways. Quantitative evidence comes from performance-based tasks (a triadic CPS task and an individual SRL task) and systematic video coding of scaffolding. Qualitative follow-up uses connected episode selection, teacher interviews, child-stimulated recall, and artifact analysis to explain quantitative patterns through joint displays and meta-inferences. The protocol contributes an operationally detailed, mechanism-oriented blueprint for evaluating how preschool PBL can foster CPS while making feasibility and pathway evidence visible.Project-based learning, Collaborative problem solving, Self-regulated learning, Teacher scaffolding, Preschool education, Sequential explanatory mixed methods

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