This study examined whether one’s temperaments and mother’s supportive/non-supportive reactions have effects on the internalization/externalization of problems related to adolescents’ problem behaviors. It also assessed the mediation effect of emotional clarity in relation to one’s temperaments and mother’s supportive/non-supportive reactions that impact children’s negative emotions. First, the internalization of problems was significantly demonstrated in adolescents with high Harm Avoidance and low Reward Dependence, and the externalization of problems was strongly predicted in those with high Novelty Seeking and low Persistence. Second, it was observed that mother’s supportive reactions to children’s negative emotions have direct effects on the internalization of problem behaviors, whereas non-supportive reactions affect the externalization of problem behaviors of adolescents. Third, the mediation effect of emotional clarity seemed to impact early adolescents’ behavior, whether with the externalization or internalization of problems, both in terms of one’s temperaments and mother’s reaction to children’s negative emotions. Thus, it can be concluded that middle school student’s problem behaviors can be impacted by one’s temperaments and his/her mother’s emotional parenting attitudes. Furthermore, the research implies that the mediation effect on emotional clarity is significant, which means that efforts to increase emotional clarity may have meaningful impact on middle school students even if their temperaments make them vulnerable to problem behaviors or their mother’s reactions to children’s negative emotions are not appropriate.