Underrepresented minorities (URMs), females, and first-generation college students declaring a science, technology, engineering, or mathematics (STEM) major face unique challenges as they transition into college; moreover, they ultimately fail to graduate with STEM majors at rates commensurate with other students. Research has shown that children's formative experiences may impact their STEM self-efficacy, interests, and identity for the rest of their academic and professional careers. This study used a thematic qualitative data analysis of 35 semi-structured interviews with Rice STEM students regarding their formative experiences. Six theoretical dimensions were developed: math perceptions, science perceptions, classroom experiences, STEM identity, exposure to STEM, and parental expectations. Participants reported low exposure to science in elementary school, strong parental influence, preferences for hands-on and problem solving tasks, and teacher support. Next steps for this research involve developing and validating a biodata measure based on these dimensions and determining its predictive validity for STEM identity and self-efficacy.