Global competitiveness of the United States is often suggested as a key outcome of developing a capable science, technology, engineering, and mathematics (STEM) workforce, a goal supported by many local, state, and national programs. Examining the effectiveness of such programs, however, may require assessment techniques that are outside their organizers' expertise. The physicists conducting the physics outreach program in the current study partnered with education researchers at the same university to achieve a more thorough measure of program effectiveness while also demonstrating how such partnerships represent an opportunity to add rigor to current evaluation. The resulting analyses demonstrated that participants in the outreach program (a) were more likely than nonparticipants to pursue an education and career in STEM, (b) were able to define and execute plans to solidify a strong foundation for pursuing a career in STEM, and (c) persisted in pursuing education in STEM after high school graduation.