Indonesia is a country with the largest Muslim population in the world. Around 202.9 million or 87.2% of its total population follow Islam as a religion. It is thus expected that there are numerous Islamic educational institutions in the archipelago. A type of such center of learning that has long existed in Indonesia is called pondok pesantren, or pesantren for short, a traditional Islamic boarding school. There, students or santris wishing to learn religion live communally in a dormitory during their schooling period. Pesantrens are estimated to first appear in Indonesia, especially the island of Java, in the 17th century. Over time many pesantrens have undergone educational changes, teaching not only religious matters but also other subjects just as modern schools. Among those pesantrens that preserve the tradition of teaching only religion is Pondok Pesantren Lirboyo that was founded in 1910 in the village of Lirboyo in Kediri, East Java Province.The founder is Kiai Haji Abdul Karim, an Islamic scholar. In an area of 19 hectare, the current number of santris at Lirboyo has reached 6 thousands, all of whom are male coming from Indonesia and beyond, such as Malaysia, Singapore, and Thailand. The education system comprises 3 grades that are based on the students’ competence instead of age.