Trust, a relational phenomenon that is an important building block of interpersonal relationships and within society, can also be an intermediary outcome of field-based environmental education programs. Trust creates a foundation for collaboration and decision-making, which are core to many ultimate outcomes of environmental education. Yet, understanding how trust develops among environmental education program participants is still nascent, partly because few methods exist for measuring trust in informal contexts, such as those that are common for many environmental education programs. Our study used social network analysis and qualitative data from focus groups, questionnaires, and participant observation to investigate the development of trust among residential environmental education program participants in two school groups, some of whom had initial familiarity with each other. Network data indicated differential increases in peer-to-peer trust among group members when measured at the individual level. Qualitative data from the focus groups highlighted salient dimensions of trust that were particularly relevant in this setting, including friendship, emotional and physical safety, and self-disclosure; reciprocal trust among peers and educators; and aspects of this immersive setting that fostered trust among the participants.