This article reports on a longitudinal test of a developmental model of early smoking that specifies reciprocal predictive relationships between smoking expectancies and smoking behavior in youth. The model was tested on 1,906 children during the transition from elementary school to middle school across 3 time points: the spring of 5th grade, the fall of 6th grade, and the spring of 6th grade. Key findings were (a) elementary school expectancies for reinforcement from smoking predicted smoking behavior during middle school; (b) smoking experience predicted increased subsequent smoking expectancies; and (c) among children who had never smoked, smoking expectancies predicted subsequent smoking onset. The finding that smoking expectancies and smoking behavior predicted each other reciprocally and positively across time in children this young may prove important in developing and refining early intervention and prevention efforts. (PsycINFO Database Record