More than half of the entering college freshmen who declare STEM majors switch out of them, especially in quantitative disciplines. This study analyzed survey data from high school science teachers and interviews with college students who switched out of quantitative STEM (Q-STEM) majors to identify (a) pull factors associated with the selection of an original Q-STEM major, (b) key events that college students experienced in their original major, and (c) push factors that contributed to the college students' decision to leave STEM. Results showed that STEM interest was associated with love for the disciplines, high school teacher encouragement, and success in academic coursework. Upon entering college, students faced a number of academic, personal, and faculty-student interaction obstacles that made students feel inadequate, unprepared and overwhelmed, resulting in them switching out of Q-STEM. Implications for student success in STEM were discussed.