Background: Through the Texas Childhood Obesity Research Demonstration study, we implemented and evaluated a system-oriented model of primary and secondary prevention approaches to mitigate obesity among low-income Texas children aged 2 to 12 years. Primary prevention included implementing the Coordinated Approach To Child Health Early Childhood (CATCH EC) program in Head Start preschools. In this paper, we describe the methods and results of CATCH EC program process evaluation over 2 years of implementation. Methods: We used a quasi-experimental design with serial cross-sectional data collected from Head Start centers across intervention and comparison catchment areas in Houston and Austin, Texas (intervention: N = 12 centers in 2012-2013 [Year 1], N = 12 in 2013-2014 [Year 2]; comparison: N = 13 centers in Year 1, N = 12 in Year 2). Process evaluation included center director and teacher surveys conducted in both years of implementation. We developed indices for implementation of CATCH EC and non-CATCH health events at the centers. Results: Implementation scores were higher among intervention centers as compared to comparison centers across both years of implementation, and these differences were statistically significant (p < 0.01). There was also high variability in program implementation in intervention centers across both years ranging from 55% to 95%. Conclusion: These implementation index strategies may inform future evaluation of preschool-based obesity prevention program implementation.