Objective: The aim of this article was to describe the nutritional status and body composition of schoolchildren from Tucumán (Argentina) and analyze variations according to sex, area of residence, and socioeconomic status (SES). Methods: A cross-sectional study was performed in 1948 schoolchildren aged 8.0 to 11.9 years. Body weight, height, triceps skinfold, waist, and upper arm circumferences were measured. Nutritional status and body composition were estimated using the NHANES III reference. SES was surveyed with the Family Affluence Scale. Area of residence was classified as urban or rural based on the criteria of the National Institute of Statistics and Censuses of Argentina. Logistic regression analysis was applied to evaluate nutritional status and body composition according to sex, area of residence, and SES. Results: The prevalence of overweight and obesity was 12.3% and 18.2%, respectively, as compared with that of underweight (2.3%), stunting (3%), and wasting (2.1%). The prevalence of stunting and wasting was higher in girls, while that of obesity was higher in boys. Low SES schoolchildren registered a higher prevalence of stunting. Analysis of body composition indicated modifications in adipose and muscular tissues, especially in undernourished (underweight, stunting, or wasting) children and children with excess weight (overweight or obesity). Conclusion: The child population from Tucumán is undergoing an accelerated process of nutritional transition, manifested by the double burden of malnutrition. The distribution of stunting, wasting, and obesity, and changes in fat and muscular tissues were not homogeneous, revealing differences according to sex, area of residence, and SES.