The imperative for bolstering engineering education at the precollege level is usually framed within the context of improving U.S. global competitiveness but this potentially cheapens the inherent value of an engineering education and obfuscates the potentially socially purposeful aspects of engineering. Drawing from design-based research, this case study examines how a project-based service-learning (PBSL) engineering design unit contributed to students’ sense of purpose in life and perceptions of engineering. It takes an ecological approach in that it considers the perspectives of students, the teacher, professional engineering mentors to understand and outline guiding principles for PBSL engineering experiences at the pre-college level. Student perspectives on the PBSL unit centered around six themes: impact of the unit; affect; meaningfulness; learning; teamwork/collaboration; and, agency. Three themes characterized student reflections on purpose in life: notions of purpose in life; student purposefulness; career aspirations. Students also discussed engineering along two broader themes of their: engineering notions and engineering interests. The educators’ (teacher and mentors) perspectives on teaching priorities and strategies for the unit aligned along seven themes: exposure; messages about engineering; hands-on/physical experience; encouraging student ideas; room for mistakes and failure; teamwork; and involving expert engineers. They identified at least six positive aspects of the unit: exposure; engineering design process and habits-of-mind; authenticity; motivation and purposefulness; student ideas; and student accomplishment. Conversely, they also discussed at least four primary areas of improvement: facilitating teamwork; adhering to design specifications and constraints; involving expert engineers throughout the process; and timing. Overall, the findings suggest that student participation in PBSL engineering units can contribute to their purpose development by facilitating opportunities for socially purposeful engagement within a STEM context. Furthermore, PBSL engineering units concretize the socially purposeful aspects of engineering, subverting wider public perceptions of engineering as a socially-unconcerned profession. Future PBSL engineering units at the pre-college level should emphasize: student input, ideas, and hands-on engagement; process over outcome, especially the engineering design process; involving the community; and, reflection.