Children need adequate and healthy nutrition for sufficient mental development and physical growth. Children also need nutrition education to gain the required skills for correct food selection. This study aimed to evaluate the effect of the child-to-child approach based on the Theory of Planned Behavior (TPB) on the eating behaviors of elementary school students in Iran. In this quasi-experimental, interventional study with pretest/posttest design and a control group, 173 fourth grade female students of public elementary schools were selected using multistage random cluster sampling. Educational intervention was performed for the intervention group through the child-tochild approach. The research data were collected in the two groups using a 5-scale researcher-made questionnaire based on the constructs of TPB with a Cronbach's alpha of 0.86 before and one and six weeks after the intervention. Then, the data were analyzed using chi-square test, repeated measures ANOVA, and independent t-test. The results showed a significant difference between the two groups regarding the mean scores of attitude, perceived behavioral control, and behavioral intention before and one and six weeks after the intervention. However, no significant difference was found between the two groups concerning the mean score of subjective norms. Moreover, the educational intervention resulted in improvement of the intervention group’s eating behaviors. The findings of this research suggested the child-to-child approach and the TPB as effective methods in improvement of correct eating behaviors in children.