This study intends to test main theories of juvenile delinquency and their relative efficacies. This work tests differential/social learning, strain, social bond, labeling, and a general theory and identifies several main explanatory factors, such as associations with delinquent peers, parental strain, strain in school, bonds with parents, commitment to scholastic activities, other's labeling, and low self-control. This study uses a panel data and also controls prior delinquency in testing the effects of seven variables on delinquency. Using KYPS data from 3,209 middle school students, results show that low self-control has the most impact on delinquency and also labeling and parental strain also appears to be important factors. However, association with delinquent peers has a weak effect on delinquency, even though its effect is significant. Those findings have mixed results, but support a relative efficacy of a general theory. The policy implication of those results are discussed.