In the fight against HIV/AIDS, the Behavior Change Communication (BCC) model stands as international best practice in preventive education. Ideally, a BCC intervention aims to changes behaviors and attitudes by facilitating group negotiation and introspection, with a resultant improvement in health. However, introducing this best practice model to a group of youth in Nairobi resulted in suboptimal outcomes: they were unaccustomed to expressing themselves in the ways prescribed by the class. To explain this failure, I examine how local discourses produced by parents and teachers communicate agency, sexuality and health, and highlight the diverging practices invoked at home, school and by the BCC model to make these youth "health conscious". At home and at school, the key commonality was the absence of any attempt to inculcate "internal" reasoning--in contrast to the BCC model. Rather, they relied on "external" pressures, through repetition, silence and behavioral discipline. Both local prevention schemes operated according to their own coherent "ideological" framework, molded by structural circumstances. Given the contextual contingency of how agency is acquired and construed, a BCC intervention may undermine overall efficiency and the host community's cultural autonomy. Ethnographic analysis is needed to enhance our understanding of local schemes and their merits, and to envision more hybrid notions of agency mediating the global and local.