The future outlook for STEM jobs in the U.S. is projected by the U.S. Bureau of Labor Statistics to have a 10.5% increase from 2020 to 2030, with 11.3 million STEM jobs projected in the U.S. by 2030. During the same time interval the projected rate of increase of STEM jobs is higher (at 10.5%) compared to non-STEM jobs (at 7.5%). Engineering, computer related jobs, mathematics, architecture, life sciences, physical sciences, scientific and technical sales, as well as the management and postsecondary teaching of these fields are amongst fields defined as STEM jobs. It is therefore important to understand what leads STEM professionals to pursue education in STEM fields and to pursue STEM careers to help guide and inform educational policy. This study examined the impact of a multiyear high school level Science Research program (SR) on program graduates' STEM college and career self-efficacy as well as on persistence in STEM college and careers and examined gender related differences. Several factors that affect these were also examined such as the impact of mentor, the impact of near-peer mentoring, the freedom to select one's own topic of research on the STEM career self-efficacy and STEM career persistence. The method was an explanatory sequential mixed methods study. The participants had graduated from the SR program between 1 and 9 years prior to the study. It was found that the SR program had a positive impact on the STEM career self-efficacy and STEM career persistence of graduates of the program. It was also found that the guidance of a mentor, near-peer mentoring, and the freedom to choose one's own topic of research had a positive impact on STEM career self-efficacy and STEM career persistence. The effects did not show gender differences. One of the surprising findings that emerged from the qualitative phase, and that supports the choice of a mixed method approach, was the importance that participants gave to guest speakers who are experts in the field and particularly alumni of the program; the participants expressed that at the time they did not feel the importance immediately but felt it later in their high school, college and careers. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]