Objective: To use and review a conceptual model of process evaluation and to examine the implementation of a nutrition education curriculum, "Choice, Control & Change", designed to promote dietary and physical activity behaviors that reduce obesity risk. Design: A process evaluation study based on a systematic conceptual model. Setting: Five middle schools in New York City. Participants: Five hundred sixty-two students in 20 classes and their science teachers (n = 8). Main Outcome Measures: Based on the model, teacher professional development, teacher implementation, and student reception were evaluated. Also measured were teacher characteristics, teachers' curriculum evaluation, and satisfaction with teaching the curriculum. Analysis: Descriptive statistics and Spearman rho correlation for quantitative analysis and content analysis for qualitative data were used. Results: Mean score of the teacher professional development evaluation was 4.75 on a 5-point scale. Average teacher implementation rate was 73%, and the student reception rate was 69%. Ongoing teacher support was highly valued by teachers. Teacher satisfaction with teaching the curriculum was highly correlated with student satisfaction (P less than 0.05). Teacher perception of amount of student work was negatively correlated with implementation and with student satisfaction (P less than 0.05). Conclusions and Implications: Use of a systematic conceptual model and comprehensive process measures improves understanding of the implementation process and helps educators to better implement interventions as designed. (Contains 5 tables and 1 figure.)