Higher education practitioners are a wide-ranging group of professionals often responsible for implementing programs and services that support student success. In this qualitative study, we examine the nature of student-practitioner relationships among a multiracial sample of 39 science, technology, engineering, and mathematics (STEM) college seniors to address three questions: (a) How do STEM students describe their relationships with practitioners on campus? (b) In what ways, if any, do student-practitioner relationships influence STEM students' feelings of marginality and/or mattering in STEM? and (c) To what extent do STEM students have different experiences based on their racial/ethnic identities? We employ a cross-case study analysis approach, contrasting the experiences of majority-status (e.g., White and Asian/Asian American) and minoritized-status (e.g., Black/African American and Latinx) students within STEM contexts. Our findings show clear differences regarding how students describe their interactions with practitioners based on racial/ethnicbackground, as well as how student-practitioner relationships impact students' sense of mattering and marginality in STEM. We conclude with implications for research and practice to address the persistent structural issues affecting STEM college students.