Underrepresentation of female students and specific racial/ethnic groups persists in STEM despite decades of intervention. Evidence suggests a need to encourage interest in STEM fields at the middle-school level. Adolescent career aspirations are influenced by exposure to role models and mindsets, such as a sense of perceived personal capacity. The purpose of this study was to measure how exposure to role models and work-based microbadging affects students' mindsets related to pursuit of STEM careers. Middle school students rated their intent to pursue a STEM career before and after completing a series of Quest-Challenge pairs featuring role models, including a biomedical engineer, in the Couragion application, along with their confidence, motivation, and enjoyment through in-app surveys. Data from students in well-represented and underrepresented STEM demographics were compared. Intent to pursue a STEM career increased after Couragion app intervention. Divided into demographic groups, increases were observed in students from underrepresented racial/ethnic groups and female students. Students reported increased confidence, motivation, and enjoyment after interacting with the app. Additionally, students reported confidence in STEM career success and motivation to apply themselves academically. This study showed increased intent, confidence, motivation, and enjoyment in middle school students related to STEM careers. The Couragion app intervention effectively improved metrics that inform students' future academic and professional decisions. Widely implementing this type of intervention during middle school could help narrow the representation gap in STEM fields.