While important for athletic development and well-being in youth sport, knowledge remains limited around the processes underpinning triadic relationships between parents, athletes, and coaches. This study aimed to examine the relational processes that drive the functioning of parent–athlete–coach triads across three developmental stages of youth tennis. Using a collective-case-study design, 10 players, 10 coaches, and 9 mothers completed preinterview tasks and semistructured interviews and provided conversational history. Reflexive thematic analysis led to the generation of two higher order themes: foundations of relationship quality and factors enabling team effectiveness. Findings highlighted how specific relationship qualities (i.e., commitment, trust, respect, and parent–coach proximity) and team effectiveness constructs (i.e., shared goals, collaborative and adjusted roles, support, and role-specific communication) served to facilitate the tennis experience for triads. Scholars are encouraged to consider integrating small-group principles (e.g., team building) into tailored support programs that address the psychosocial needs of the triad.