ABSTRACT: This quasi-experimental study assessed impact of factors associated with classroom implementation of health curricula by North Carolina teachers. School representatives selected and implemented one of three tobacco prevention curricula — Project SMART, Growing Healthy, or the Teenage Health Teaching Modules — in either sixth or seventh grades. Prior to implementation, experimental teachers and administrators received extensive curricula training. Implementation data were collected through teacher completed checksheets and classroom observations for two time periods — initial implementation (n = 69) and maintained implementation (n = 136). While training was associated significantly with whether teachers implemented a curriculum (p < .05), other factors also were important. Variables outside of teachers' direct control, such as supportive administrators, context in which health instruction is taught, and turbulence, affected quantity and quality of curricular implementation.