This dissertation examines children’s development of self-regulation during the elementary school years by applying longitudinal measurement and latent variable models to classroom teacher ratings of children’s effortful control (EC) and direct cognitive assessments of children’s executive functions (EF). Self-regulation is known to support success in school, but research findings vary depending on whether capacities are defined in terms of behavior or cognition, operationalized with direct or indirect assessment, and framed in terms of developing attributes or stable traits. EC can be considered a temperamental characteristic that is theorized to manifest in relative stability over time and is often measured with adult report, whereas EF normatively improves during the early and middle childhood years and is typically assessed via performance on novel tasks. The nature of these constructs within a given child is of particular import, such that intra-individual development can be disentangled from inter-individual differences.Therefore, this project draws on data from the national Early Childhood Longitudinal Study, Kindergarten Cohort of 2010-2011 (ECLS-K) to address three primary research objectives: (a) establish the psychometric properties of EC as assessed in the ECLS-K and generate corresponding longitudinal scores, (b) examine children’s typical trajectories of change and/or stability in EC from kindergarten to fifth grade, and (c) explore heterogeneity in the co-development of EF and EC during this period. Results show that EC has a unidimensional structure that is suitable to longitudinal linking, and can therefore be used to measure children’s individual development over time. Subsequent longitudinal models indicate that EC is generally characterized by intraindividual stability rather than change, and meaningful interindividual variation in EC reveals three latent subpopulations of change that are distinguishable by level and/or shape. The final set of analyses reveal no systematic relations between growth in EF and development of EC, regardless of age group (younger versus older children) or the model employed. Findings are discussed with regard to developmental theory and methodological implications.