The development of interest and aspirations to pursue STEM careers has been a focus of recent educational research and action. This study used Social Cognitive Career Theory as the framework to explore how types of learning experiences in and out of school prior to college affected undergraduates' STEM beliefs and intent to pursue a career in a STEM field. A sample of 312 students at a large university were surveyed about the experiences in which they had participated, their perceptions of those experiences, and their self-efficacy, outcome expectations, and interests in science, mathematics, and engineering. The results indicated experiences that predicted beliefs across all STEM areas, but also some key experiences that differed depending on the subject. Experiences revolving around family and career-specific activities were important for science and engineering beliefs, the opportunity to build and create was important for mathematics and engineering beliefs, and varied instructional techniques were valuable for mathematics and science beliefs. This paper details the relationship between these experiences and STEM beliefs and career choices along with recommendations for educators looking to develop experiences to enhance STEM career pathways.