While most current research in teaching and learning is performed in the classroom, evidence suggests that the quality of a student's learning is also affected by experiences outside of the classroom (i.e. extra-/co-curricular experiences). Engineering students in particular have available to them a rich variety of learning opportunities outside of the classroom - such as competition teams, undergraduate research experiences, and service learning organizations - which reinforce and strengthen the knowledge they gain through engineering coursework. The goal of this project is to determine the impact of engineering students' participation in extra-/co-curricular activities on their development into professional engineers. Understanding the specific benefits that engineering-focused extra-/co-curricular programs offer to students will allow those in career and academic advising positions to provide targeted advice to students on how to personalize their pathways through college engineering program, focusing on topics that are interesting to them and finding avenues for strengthening existing skills or learning new ones. The extra-/co-curricular setting also gives students a relaxed, enjoyable opportunity to practice engineering skills in an authentic environment, leading to improved confidence - a feature that is particularly important for students from underrepresented groups in engineering - and a more technically competent engineering workforce. Further, although certain features of the engineering-focused extra-/co-curricular experience may be challenging to reproduce in a classroom setting, other features may provide inspiration for alterative teaching practices which can enhance learning within the classroom.<br/><br/>This project answers two fundamental research questions: (1) What specific features of students' academic and professional development are affected by engineering-focused extra-/co-curricular participation, and (2) What specific features of extra-/co-curricular activities most influence students' academic and professional development' The research has a two-phased design where the first phase implements the Statics Concept Inventory, the Engineering Professional Skills Assessment, and a self-efficacy survey to measure achievement of learning outcomes including mastery of fundamental engineering concepts, development of professional skills, and self-efficacy. In the second phase, participants from Phase 1 are recruited for interviews in order to uncover possible explanations for the research findings in Phase 1. The approach used in this work will lay the groundwork for other scholars in non-engineering disciplines to perform assessments of their own discipline-specific extra-/co-curricular activities to determine if similar patterns exist. The framework used in this research will also allow other scholars to explore factors related to engineering-focused extra-/co-curricular participation which are not covered in this research, for example, determining how the extra-/co-curricular experience uniquely affects engineering students from underrepresented groups.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.