With regard to adolescents' sense of the academic competence, one study found that lower- to upper-middle class students who experienced an increase in academic self-concept between 7th and 9th grade tended to experience a sizeable increase in intrinsic motivation over this period (Harter et a., 1992). In contrast, those who did not experience a change in academic self-concept experienced only a slight increase, and those who experienced a decline in self-concept experienced a decline in achievement motivation over this same period. This finding occurred even while controlling for earlier levels of academic self-concept, allowing the authors to all but rule out that the relationship between academic self-concept and achievement motivation was due to selection effects.