To meet the demand of the growing science and health sectors in the United States, there is a critical necessity to engage more people in science, technology, engineering, and math (STEM). To broaden participation in STEM, we must understand the factors that shape perspectives and beliefs around career selection. Good measurement of these factors is crucial to quantify how effectively educational interventions impact student attitudes towards STEM. Adolescents are particularly suited for quantifying intervention efficacy because students build their identities during these formative years and make important career choices. To better quantify intervention efficacy at the high school level, we developed an instrument entitled Student Attitudes Surrounding STEM (SASS), which builds upon the social cognitive career theory (SCCT) framework for understanding career selection. Questionnaire responses were collected from 932 high school students, and split into samples of 400 for exploratory factor analysis and 532 for confirmatory factor analysis. The questions clustered into six factors: self-efficacy experience, self-efficacy academic, outcome expectations, interests, negative perceptions of scientists, and career awareness. The SASS exhibited adequate construct validity as determined by fit indices and theoretical considerations. Furthermore, the instrument demonstrated criterion validity, internal consistency, and test-retest reliability. This tool represents a novel integration of three latent variables into SCCT, negative perceptions of scientists, career awareness, and an experience factor for self-efficacy.