Self-efficacy is seen as a barrier for youth, females in particular, to enter computer science (CS). In this study, I presented a near-peer mentoring model that focused on changing the mentee's self-efficacy in CS. The present study had three objectives: (a) to design a near-peer mentoring model (i.e., a conceptual model) around the sources of information that influence self-efficacy, (b) to develop a mentor training model based on the conceptual model, and (c) to test the effectiveness of the training model in increasing mentees' self-efficacy in the context of a summer App programming camp. The present study adopted a mixed-methods approach following a concurrent, embedded design to answer research questions. Data were collected from pre-post surveys and camper interviews. Comparison of quantitative and qualitative findings indicated that the near-peer mentoring model has a potential in increasing youth's self-efficacy regardless of their gender. It was also found that encouragement was important for fostering self-efficacy and while they did not directly influence self-efficacy, modeling and instructive feedback enhanced campers' learning experience, which, in turn, would boost self-efficacy. The present study also provided examples of how to train mentors to do modeling and provide instructive and encouraging feedback, which may be helpful for programs that use mentors to recruit youth to CS. [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.]