Examining school-level implementation of British Columbia, Canada's school food and beverage sales policy: a realist evaluation.

Objective: To identify key school-level contexts and mechanisms associated with implementing a provincial school food and beverage policy.

Design: Realist evaluation. Data collection included semi-structured interviews (n 23), structured questionnaires (n 62), participant observation at public events (n 3) and scans of school, school district and health authority websites (n 67).