Design principles, development and adaptation of a large-scale intervention study in Denmark

Departing from a newly developed phenomenological inquiry-based approach to literature, this article
examines the process of designing, developing, and refining a large multi-pronged intervention program
in Danish lower secondary schools (86 schools, 265 classes, 5531 students), including randomized controlled trials in 72 schools. In order to offer greater insight into the complex causality between design,
process, output, and outcome, the intervention process is described by means of an initial program theory, a pre-study with three reviews of available evidence and practice, and a Design Based Research (DBR)
process with iterations and interconnected phases: small-scale interventions, a pilot study, and three
rounds of large-scale interventions with randomized controlled trials with different samples. This article
focuses particularly on the crucial decision points at which participants change their role and redesigns
contribute to a deeper insight into the social mechanisms of the complex intervention.