Reflection involves active, persistent, and careful consideration of any belief or practice. It promotes understanding of underlying beliefs and application of new knowledge to new situations. Problem-Based Learning (PBL) provides the instructional mechanisms for prompting learner reflective thinking. Research questions for this study were: (1) What are the factors that students perceive as prompting reflective thinking? (2) Which factor is perceived as the most important for prompting learners' reflective thinking? (3) Is there a significant difference between the derived factors? and (4) Which elements or characteristics prompt reflective thinking within the derived factors? Participants were 144 students in grades six through eight who attended three different middle schools in rural Pennsylvania. This study found that young students perceived three factors as most important in supporting their reflection in PBL lessons: learning environment, teacher, and scaffolding tools. Reflective activities are described and implications for designing PBL are discussed. (Contains 20 references.) (Author/AEF)