This study investigated the difference in specific internship program outcomes of undergraduate Science, Technology, Engineering and Math (STEM) work-integrated learning (WIL) experiences as a function of the length of the experience. The study employed analysis of archival data representing a sample of over 1,000 undergraduate STEM students who completed at least one summer or semester internship with a single, research-focused government agency. Internship outcomes in relation to four constructs were investigated: (a) work-skills development, (b) workplace self-efficacy, (c) academic self-efficacy, and (d) retention. The z-Test for Proportions was used as the basis of the analyses. The self-identified influence of these experiences on work-skills development, work self-efficacy, and academic self-efficacy was determined through analysis of intern responses to an end-of-experience survey. To investigate retention outcomes, data collected from longitudinal tracking of the students who participated in these internships was used to identify differences in successful entry into the STEM workforce. While there is some indication that even the small difference in length between 10 week summer and 15 week semester internships can lead to increased outcomes, overall results were inconclusive. This study suggests that further investigation of experience length is necessary. However, results support the use of self-efficacy theory in shaping policies to maximize outcomes of work-integrated learning experiences, both for managers of academic and employer WIL programs. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]