Background: Studies of body mass index (BMI) change have focused on understanding growth trajectories from childhood to adolescence and adolescence to adulthood, but few have explored BMI trajectories solely in elementary (grades K-5) school children. This report complements these studies by exploring changes in obesity status using analytic methods developed to investigate categorical changes in life-course events. Methods: Sequences of a 4-state BMI variable (underweight, normal, overweight, and obese) were calculated using height and weight data collected annually (2008-2013) from 414 kindergarten and first-grade students participating in the Community and Schools Together (CAST) project. These sequences were explored using the TraMineR software package to investigate the distribution of sequences and states, calculate transition rates among states, and examine clustering of sequences. Results: Aggregated cluster solutions were identified consisting of either 4 clusters (normal, stepped, mixed, and obese) or 3 clusters (aggregation of obese cluster cases into stepped cluster) with membership in the former predicted by ethnicity and socioeconomic status (SES) and the latter by SES alone. Transition rate patterns among states varied markedly by cluster and state. Conclusion: The finding of early emergence of stable obesity states, especially in Hispanic children confirms the need for early childhood interventions to influence BMI.