Background: Black adolescents commonly experience unfair treatment from teachers and other school staff that can undermine Black adolescents' engagement in school and their perceptions of adults as trustworthy. Objective: This study aimed to address the overarching research question: "How do unfair experiences with school staff manifest and impact Black adolescents?" Method: This study used a mixed methods approach guided by two sub-questions. Our qualitative strand of inquiry used interview data from 25 Black adolescents, their parents, and another familial adult (75 total interviews) to explore the sub-question: "How do unfair experiences with school staff unfold?" Our quantitative strand analyzed survey data from 216 Black adolescents to address the sub-question: "Is a specific type of unfair experience, teacher racial discrimination, associated with Black adolescents having fewer natural mentors (supportive non-parental adults from adolescents' everyday lives) via lower trust toward adults?". Results: Analyses of interview data suggested experiencing specific types of unfair treatment-- (a) being singled out, (b) observing favoritism, (c) feeling belittled, and (d) unwarranted or overly harsh punishment--was followed by students disengaging from class, schoolwork, or teachers. Analyses of survey data indicated unfair treatment in the form of teacher racial discrimination was negatively associated with the quantity of natural mentors via lower perceptions of adults as trustworthy. Conclusions: Collectively, our findings suggest unfair treatment by school staff may set in motion a domino effect that negatively influences Black students' engagement with school and undermines their connection with supportive adults.