Possible links between lower birth weight, childhood diet, and learning in Taiwan are evaluated. The population representative Elementary School Children's Nutrition and Health Survey in Taiwan 2001-2002 and the national birth registry were used to examine school and social performance using the modified Scale for Assessing Emotional Disturbance questionnaires in relation to diet quality by the Youth Healthy Eating Index-Taiwan and birth weight of children aged 6-13 years (n = 2283). Lower birth weight (less than or equal to 15th percentile: less than or equal to 2850 g for boys and less than or equal to 2700 g for girls) children were mostly from mountainous areas and of indigenous descent. Compared to normal birth weight, lower birth weight girls experienced greater inability to learn and weaker overall competence. Better diet quality predicted more favorable emotional and behavioral outcomes in lower birth weight girls, and this persisted with adjustment for covariates. None of these findings were evident among boys. Girls' cognitive and social development appears to be susceptible to diet quality and birth weight, such that the adverse risk of lower birth weight on school performance may be offset by improved diet. (Contains 4 tables and 1 figure.)