Immigration from Turkey was the primary reason for the rapid increase in the number of Muslims living in Germany. Over the years, the Muslim community developed into the second largest religious group in the country. Still, no regular instruction in Islam was introduced into German schools, since the diversity of Islamic beliefs and the organizational splintering of Muslims in the Federal Republic prevented the official recognition of Muslims as a religious community. Additionally, there were concerns about the compatibility of the Koran with the values of the Basic Law of the Federal Republic. Therefore, Muslims had to organize their own private religious instruction; in many cases, they sent their children to Koran courses offered by Islamic organizations.