Identity development frameworks provide insight into why and to what extent individuals engage in STEM-related activities. While studies of "STEM identity" often build off previously validated disciplinary and/or science identity frameworks, quantitative analyses of constructs that specifically measure STEM identity and its antecedents are scarce, making it challenging for researchers or practitioners to apply a measurement-based perspective of participation in opportunities billed as "STEM." In this study, we tested two expanded structural equation models of STEM identity development, building off extensions of science and disciplinary-identity frameworks, that incorporated additional factors relevant to identity development: gender, ethnicity, home science support, parental education, and experiencing science talk in the home. Our models test theorized relationships between interest, sense of recognition, performance-competence, and identity in the context of STEM with undergraduate students (N = 522) enrolled in introductory STEM courses at a Hispanic Serving Institution. Our findings support our measurement of STEM identity and its indicators, providing researchers with a predictive model associated with academic intentions across disciplinary domains in STEM. Further, our expanded model (i.e., Model I+) indicates significant contributions of participant gender, which has a larger indirect effect on STEM identity ([beta] = 0.50) than the direct effect of STEM interest ([beta] = 0.29), and of home support in relation to performance-competence in academic contexts. Our model also posits a significant contribution of family science talk to sense of recognition as a STEM person, expanding our understandings of the important role of the home environment while challenging prior conceptions of science capital and habitus. We situate our results within a broader discussion regarding the validity of "STEM identity" as a concept and construct in the context of communities often marginalized in STEM fields.