Frequent and often contradictory directives were issued by Interior Minister Wilhelm Frick, Bernhard Rust of the Reich Ministry of Science, Education and Culture, and other agencies regarding content of lessons and acceptable textbooks for use in primary and secondary schools.[349] Books deemed unacceptable to the regime were removed from school libraries.[350] Indoctrination in National Socialist thought was made compulsory in January 1934.[350] Students selected as future members of the party elite were indoctrinated from the age of 12 at Adolf Hitler Schools for primary education and National Political Institutes of Education for secondary education.