The juku provide supplementary education for students who need additional help with their regular school subjects, and for students who are studying for entrance exams. Most juku courses are held during the after-school hours or on Saturday morning.
Variations of the juku exist in most developed countries. In Japan, however, these institutions are far more numerous, and are attended by a far wider range of students. This is because of the highly competitive nature of the Japanese school system, and its heavy reliance on standardized examinations.