Worldwide, engineering design is seeing an increase in pre-college settings due to changing educational policies and standards. Additionally, these projects can help students develop critical skills for a broad range of problem settings, such as design thinking and reflection. In design and other contexts, reflection is a mental process where someone returns to previous experience and uses this revisiting to aid in new actions. While there is substantial research studying design practices at the collegiate or professional level, the design practices of younger students remain understudied. Moreover, past research on reflection has tended to focus on how to support reflection or what impact reflection has and not how students engage in reflection strategies. We had 105 middle school students in the Midwestern United States design a green-energy home using a computer-aided design (CAD) tool, Energy3D. Students were instructed to use Energy3D's design journal to reflect on their design process throughout the project, enabling students to employ different reflection strategies. Energy3D unobtrusively captures students' design actions, including journal interactions; these were used to identify students' reflection strategies. Three features of journal interaction were developed, i.e., frequency of interaction across sessions, intensity of interaction, and relative frequency of journal use over other actions. We used k-means cluster analysis on these features and discovered four groups representing different strategies. Regression was used to understand the relationship between reflection strategies and design outcomes. Finally, we draw out implications for supporting pre-college students' productive beginnings of engagement in reflection and future study directions.