„Compared to the Japanese juku industry that generates about $ 12 billion a year, the institutionalized German Nachhilfe system with its estimated more than 4,000 Nachhilfe schools is in an early stage of development.“
Steve Entrich, Effects of investments in out-of-school education in Germany and Japan. In: de Gruyter, Contemporary Japan, 2014, 26(1), S. 77.