This explanatory mixed methods study investigates the experiences of approximately 280 rural, underrepresented middle school student members of STEM Career Clubs over 3 semesters (19 meetings). Data sources included surveys about STEM interests and career intentions (STEM-CIS), STEM club perceptions, and content questions. A subset of 101 students were interviewed. Students found the club an important, positive experience and the staff caring and knowledgeable, although there was no growth in their STEM-CIS scores. Students who attended meetings regularly (>10 meetings) demonstrated higher initial STEM-CIS scores and better content knowledge than students who attended sporadically. Students' subjective task value (e.g., enjoyment, utility, cost, interest), identity, and key socializers were motivational factors most expressed as influencing students' learning and STEM intentions.