This study examined the new self-report version of the Strengths and Difficulties Questionnaire (SDQ-S), SDQ-Kids, in primary school children regarding internal consistency, teacher-child agreement, and validity. Data from 2,655 children in Grades 1 to 3 and their teachers were analyzed. Children completed SDQ-Kids, previously piloted (n = 896), while teachers completed SDQ-T. Reliability was measured using Cronbach’s alpha, and logistic regression analyzed the association between rating source (teachers vs. children) and SDQ status (“abnormal” vs. “normal”). Validity was assessed using Pearson’s correlation coefficient. SDQ-Kids showed acceptable internal consistency for total difficulties (α =.77) but lower for subscales (α =.40–.68). SDQ-T reliability was good for total difficulties (α =.90) and acceptable to good for subscales (α =.78–.89). Differences emerged, particularly in internalizing and externalizing problems. Correlations of SDQ-Kids with other instruments were acceptable to low. Differences between teacher and child reports highlight the need for a multi-informant approach. While SDQ-Kids’ total difficulties showed acceptable reliability, scale-level reliability and validity were unsatisfactory.