Research on the development of childhood internalizing problems has largely failed to consider that there may be different developmental paths for boys and girls. Additionally, studies have begun with elementary school children who are well beyond their first social experiences. This study follows 144 boys and 125 girls from kindergarten (for most children the time of first social experiences) to fifth grade. We identify the best predictors of fifth grade internalizing problems from kindergarten measure of anxiety-withdrawal, shyness, adaptability, and popularity. We also test whether maternal overprotectiveness moderates the link between kindergarten predictors and fifth-grade internalizing problems. Throughout, we consider boys and girls separately. Peer-rated unpopularity was the best predictor of later problems for both boys and girls, followed by peer-rated shyness for boys and teacher-rated anxiety-withdrawal for girls. Maternal overprotectiveness was more important for boys than girls. For boys overprotectiveness reduced the predictive link between some kindergarten variables and some fifth-grade outcomes; for girls overprotectiveness did not significantly moderate the predictive link. We discuss the advantages of different perspectives (peers, teachers, and mothers) for predicting internalizing problems. We also discuss the roles of early temperament, early social experience, and maternal overprotectiveness versus close temporal experience in developing internalizing problems.