The purpose of the present study was to examine the relationship between supplimentary after-school private institute coaching, academic motivation, and achievement of elementary school children, specifically, to examine the differential influence of the types of subject areas, duration of attendance, and hours per week on childrens' intrinsic satisfaction, task challenge level, self-regulatory efficacy, and academic achievement. Responses on a questionnaire for informations about after-school private institute coaching experience and academic motivation from 267 5th graders in a public elementary school in Seoul were analyzed. Results from the 1997 national achievement test were used as childrens' academic achievement scores. The results of the present study showed that the duration of coaching institute attendance was positively correlated with self-regulatory efficacy(r=.22), and with academic achievement(r=.21). Also, the weekly attendance hour was positively correlated with academic achievement(r =.23). There were significant positive correlation between all the motivation variables and academic achievement(r=.20~.40). There were no differential effect of the subject areas and weekly attendance hour on children's academic motivation. However, the different durations of coaching institute attendance showed differential effects on children's self-regulatory efficacy and task challenge level, i.e., the longest attending group showed the highest on the self-regulatory efficacy and the task challenge level. Multiple regression analysis with all variables entered in the model showed that the duration of attendance, task challege level, and self-regulatory efficacy were potent predictors of academic achievement. These results suggest that the institute coaching is not as effective as is commonly expected. Rather, the fact that motivation variables are most importantly related with high academic achievement is confirmed again.