Juveniles in institutional treatment lack the skills to cope with societal expectations, rules, and moral values. If not prevented by staff, bonds are established with other deviant youth and the placement serves as a perfect "school of crime." This article aims to explore staff strategies to prevent negative peer cultures, as well as their theoretical foundations and relation to staff academic level and professional experience. Data were collected at eight Swedish institutions, using the Correctional Program Assessment Inventory 2000, questionnaires, observations, and interviews with clinical staff. Results show that most facilities lack negative-peer-culture strategies, but this is not related to academic level or experience. The importance, in terms of influencing the residents, of theoretical knowledge concerning psychological group-processes, peer culture, and moral development, as these relate to staff-supervised or unsupervised time, is discussed.