This prospective, mixed-method study presents an in-depth view of school-based youth mentoring relationships using qualitative data from direct observations, in-depth interviews, and open-ended questionnaires with mentors and students. The dimension of interpersonal tone, referring to the interaction style between adult mentor and student, was investigated using a pattern-oriented approach. The analyses identify four distinctive patterns of interpersonal tone and categorize mentor–student relationships according to systematic variation on this dimension. The study integrates quantitative assessments of relationship quality to corroborate and supplement these inductively derived categories. Findings reveal meaningful distinctions in the nature and quality of mentoring relationships and suggest implications for the supports programs might offer to promote positive relationships.