Semester schools provide high-school students with a relatively new type of learning environment that largely has not been empirically studied. This study used a retrospective survey (n = 797) to explore the learning outcomes that stem from semester schools and identify features within the educational environment that promote them. Participants reported that appreciation for differences was the most critical and useful outcome of participation in semester school programming, with willingness to try new things, communication and identity development following closely behind. Participants also identified specific features of semester schools that supported the development of their learning outcomes, which included relationships with faculty and peers, the pedagogical approach used by semester school teachers, the non-traditional structure of the semester, and specific coursework or learning activities. The findings pointed to the strong community that developed between students and their peers, as well as to their teachers as being a driver of the intrapersonal development participants experienced, which partially stemmed from the distinct features of semester schools such as being away from home, living together in a bounded social structure, and having an integrated curriculum. In addition, the temporary structure of a semester school could promote types of learning that students would not typically experience while at traditional four-year high schools.