A co-curricular program was initiated to increase the opportunities for engineering undergraduates to engage in self-directed and industry-relevant learning. The program included three track options: professional certifications, design projects, and entrepreneurship training. The goals of the program are to increase degree completion, industry employment, and engineering career success of undergraduate student, especially those from underrepresented, first-generation, and low socioeconomic status backgrounds. This study investigated the connections between student-reported social-psychological traits, namely engineering identity and self-efficacy, and participation in the co-curricular program during its first three semesters of implementation. The purpose of the study is to understand the mechanisms by which program components may or may not improve student retention and employability outcomes. Pre and post surveys were administered to program participants upon their entry into the program and upon completion of their certificate, project, or training. Surveys included previously-validated scales for self-reported engineering identify and self-efficacy. Nearly all survey respondents completed the professional certification or design project track. Program participation significantly increased engineering identity, especially for the sub-scales for recognition as an engineer and competency as an engineer. A positive trend was observed for engineering self-efficacy but was not statistically significant. Active engagement in engineering-related design and self-directed study facilitated by the co-curricular program increased self-reported engineering identity, a social-psychological trait linked to persistence in engineering.