Designing Participatory Systems Interventions for Behavioural Change: Integrating Soft Systems Methodology, the Theory of Planned Behavior, and Experiential Learning

Small and medium‐sized enterprises (SMEs) operate within complex sociotechnical systems where behavioural change is shaped by interdependent cognitive, social and structural factors. This study examines a participatory systems intervention with food and beverage SMEs in a coastal tourism context in Vietnam. The intervention integrates Soft Systems Methodology, the Theory of Planned Behavior and LEGO SERIOUS PLAY, using single‐use plastic reduction as a context for systemic learning and capability development. Thirty‐six participants engaged in experiential, facilitated activities to articulate problem boundaries and co‐create feasible change pathways. Pre‐ and post‐intervention surveys assessed self‐reported changes in attitudes, subjective norms, perceived behavioural control and behavioural intentions. Results show statistically significant improvements, particularly in perceived behavioural control and subjective norms. The study examines these psychological determinants as intermediate mechanisms within systems‐based cleaner production transitions, illustrating how behavioural theory and participatory sensemaking can support systemic inquiry and stakeholder alignment in practice.