This paper attends to the critical, problematic and massively pervasive question of moving from precise and defensible statements of theoretical validity to equally precise and defensible statements of practical viability. Specifically, the paper presents certain experiences of sociologists engaged in bringing to bear tested propositions of youth development (or, in a more restrictive sense, juvenile delinquency) on the routine institutional practices of schools, courts, police, social services and families. The primary focus is on deliberate and theoretically-guided social change, and the practical and social conditions of its occurrence. (Author)