In this study, I examined the mal-adaptability in the tendency to over-adaptation among the junior high students from the viewpoint of self-discrepancy theory and diathesis stress theory. The discrepancy between ideal self and the reality self lets an individual invoke certain cognitive dissonance. When this cognitive dissonance occurred, stress reaction and school phobia feelings were higher in those who have high tendency to over-adaptation. In addition, when a stressor was low, the tendency to over-adaptation did not influence a stress reaction, but when high, tendency to over-adaptation developed stress reaction in boys but not in girls.