Oppositional and defiant behavior (ODB) problems are among the most important behavior problems in school children. Understanding their trajectories during elementary school and conditional risk factors at school entry is essential for implementing effective preventive and corrective interventions. Behavior problems of a population sample (958 boys, 971 girls) attending public schools were assessed annually by teachers. Three groups were identified: High Opposition (HO; 14.5%), Moderate Opposition (MO; 37.5%), and Low Opposition (LO; 48.0%). Children on the HO trajectory were found to be different from those on the MO and LO trajectories for numerous kindergarten risk factors: a) they tended to be boys with high family adversity; b) their mothers reported low warmth and high control; c) teachers rated them high on physical aggression, opposition, hyperactivity and low anxiety. Children who are likely to have chronic ODB throughout the elementary school years can be identified in kindergarten. Preventive interventions at school entry could probably help these children.