<p>The twenty-first-century economy has created an increasing demand for STEM education to prepare students for STEM careers. An emerging example is selective STEM high schools – institutions primarily focused on recruiting high-achieving students interested in pursuing and persisting in STEM fields. While theories of identity development have helped explain how students identify with STEM and how institutional factors relate to this process, further analysis is needed to understand the different contexts within which students who identify with and persist in STEM operate. This study analyzes how twenty-eight students who applied to selective STEM high schools conceptualized and identified with STEM in their first year of postsecondary education in the United States. Interviews were conducted with students who attended selective STEM-focused high schools and those who did not attend or had discontinued attending such schools. Using a phenomenological approach, we examined how students’ self-reported high school experiences relate to their conceptualization and perceptions of interest, recognition, participation, and competence in what it means to be a STEM person. Findings suggest that selective STEM-focused high school experiences gave students a more nuanced understanding of STEM fields. However, students also shared perceptions of incongruence with their interests perceived as unrelated to STEM, continuous stress and mental overload, and antipathy toward mathematics.</p>