Anemia affects approximately 25% of school-aged children (SAC—aged 5.00–14.99 years) globally. We determined in three countries the prevalence and determinants of anemia in SAC. Data on sociodemographics, inflammation and nutrition status were obtained from the 2006 Mexican National Nutrition Survey, the 2003-6 US National Health and Nutrition Examination Surveys, and the 2010 Encuesta Nacional de Nutrición Situación Colombia. In the US, vitamin A and iron deficiency (ID) were available only for girls aged 12.00–14.99 years to which our analysis was limited. Associations were evaluated by country using multivariable logistic regression adjusting for confounders and complex survey design. The prevalence of anemia and ID were: Mexico 12% (ID 18%), n = 3660; US 4% (ID 10%), n = 733; and Colombia 4% (ID 9%), n = 8573. The percentage of anemia associated with ID was 22.4% in Mexico, 38.9% in the US and 16.7% in Colombia. In Mexico, anemia was associated with ID (adjusted OR: 1.5, p = 0.02) and overweight (aOR 0.4, p = 0.007). In the US, anemia was associated with black race/ethnicity (aOR: 14.1, p