On completing middle-school (ninth grade), Israeli students must choose which discipline(s) to major in upon entering high school. This study, grounded in Expectancy-Value Theory (EVT), identified and modeled the factors that contributed to students' academic choices from their own subjective perspectives. We collected qualitative and quantitative data from ninth graders in two urban middle-schools (n=295) at the school year's end. We found that (a) most students cited interest and utility value as their main motivations for choosing a science, technology, engineering, and mathematics (STEM) major, expectancies were mentioned less; (b) students who chose a STEM major had statistically significant higher scores for EVT's key predictor variables (personal attributes, "subjective task value," "expectation of success," perceived effects of environmental factors) than their counterparts who majored in non-STEM disciplines; (c) the positive perceptions of their peers' interest and ability in science contributed significantly to students' choice to major in STEM disciplines; and (d) no significant gender differences re academic choice were found. One highly unexpected finding emerged: Participation in advanced science programs for highly qualified students ("ability grouping with curriculum differentiation") was by far the most significant factor in the choice to major in STEM disciplines. This finding has major implications for science education policy and practice.