Reflecting international debates on grounding professional practice in evidence, Sweden was the first country to incorporate policies for education based on scientific foundation and proven experience into school law. In contrast to this legal obligation in formal schooling, non-formal adult education institutions such as the folk high schools (FHS), and specifically their youth recreation leader programme, have adopted similar policies rooted in ideals of ‘free and voluntary’ popular education. This article identifies how policy actors – the government, the National Board of Education, the National Council of Adult Education, and the Youth Recreation Leader Schools – have shaped these policies over time by tracing their articulations in official documents from 1974 to 2024. Drawing on curriculum theory, we analyse what counts as valid knowledge, how and why it is selected, and by whom. The results demonstrate how these actors shape two shifts in policy formation over the period: from a knowledge focus grounded in proven experience to one emphasising scientific foundation, and from a knowledge rationale focus on commonality across programmes to one oriented towards quality. These shifts show how FHS self-governance reworks quality through scientific foundation and negotiates what counts as valid knowledge while also legitimising these policies and the programme.