This study was conducted to explore the effects of novelty seeking temperament and harm avoidance temperament on school adjustment in middle school students and to investigate the mediating effects of emotional regulation on the relationship between temperament and school adjustment. A survey was conducted on a random sample of 672 middle school students. Data were analyzed using PASW ver. 18.0 and AMOS ver. 18.0 to carry out descriptive statistics, correlation analysis, and the structural equation model. The main results of analysis could be summarized as follows. First, novelty seeking temperament and harm avoidance temperament had a negative influence upon school adjustment in middle school students. Second, emotional regulation had a positive influence upon school adjustment in middle school students. Third, temperament acted as a partial mediator for emotional regulation affecting school adjustment in middle school students. The study contributes to the literature by providing fundamental insights into school adjustment in middle school students.