As internalizing and externalizing problems often co-occur, the current study utilized a longitudinal dataset of 784 at-risk children (predominantly from low-income families and academically at-risk; 52.6% male) followed yearly from Grade 1 to Grade 12 to: (a) explore the heterogeneity in the codevelopment patterns of internalizing and externalizing problems by using a person-centered approach, and (b) investigate early childhood antecedents that might explain differentiated codevelopmental patterns. The antecedents consisted of individual (i.e., ego-resilient personality, intelligence, language ability, gender, and ethnicity) and contextual factors (i.e., maternal support and responsiveness, family socioeconomic adversity, teacher-child relationship conflict, and peer rejection). We identified 4 distinct codevelopment patterns including a chronic co-occurring group (30.1%), a moderate co-occurring group (28.5%), a pure-externalizing group (18.6%), and a low-risk group (22.8%). While children who belonged to any of the 3 higher risk groups exhibited more adverse early childhood antecedents compared with the low-risk group, the chronic co-occurring group displayed the most severe profiles of early childhood antecedents compared with the moderate co-occurring and the pure-externalizing groups. Common antecedents for the 3 higher risk groups were lower ego-resilient personality, higher teacher-child relationship conflict, being male, and being African American. Low language ability and peer rejection were identified as unique antecedents for the chronic co-occurring group.