Purpose: Measurable results of efforts to teach empathy to engineering students are sparse and somewhat mixed. This study's objectives are (O1) to understand how empathy training affects students' professional development relative to other educational experiences, (O2) to track empathy changes due to training over multiple years, and (O3) to understand how and what students learn in empathy training environments. Methods: Students in a multiple-semester empathy course completed surveys ranking the career development impact of the empathy program against other college experiences (O1), rating learning of specific empathy skills (O2), and ranking program elements' impact on empathy skills (O3). Intervention and control groups completed the Interpersonal Reactivity Index and Jefferson Scale of Empathy at four time points (O2). Cohort students participated in post-program interviews (O1, O3). Results: O1--Empathy training impacted career development more than several typical college activities but less than courses in major. O2--Students reported gains in four taught empathy skills. Cohort students showed significant increases in the Jefferson Scale while the control group did not. There were no significant changes in Interpersonal Reactivity Index scores. O3--interactive exercises had a significant effect on students' learning all empathy skills while interactions with people with disabilities had significant effect on learning to encounter others with genuineness. Students valued building a safe in-class community facilitating their success in experiential environments. Conclusions: This study highlights empathy skills' importance in engineering students' development, shows gains in empathy with training, and uncovers key factors in students' learning experience that can be incorporated into engineering curricula.