This explanatory case study aims to investigate conceptual changes on the part of gifted and talented students and describe their reflective thinking with regard to problem-solving as part of the problem-based learning (PBL) process. Twenty-two gifted and talented fourth grade primary school students participated in the study. The students were taught with problem-based science modules for eight weeks. The data collection tools used were "structured reflective diaries with regard to problem-solving" and a "semi-structured interview form with regard to conceptual learning". Data analysis revealed that the PBL enriches the conceptual science learning of gifted and talented students. The reflective thinking of such students with regard to problem-solving was mostly involved questioning and evaluation. In their diaries, the students' reflections included explanations of, and questions about, the issues and concepts in the problem-solving process, evaluations of the comparison of solutions among their peers, and new problems in the subject area. However, students only explained the operations they performed in solving the problem superficially. Therefore, students' reflections, which included their awareness of the activities they had performed as part of PBL, were limited.