As I understand it, Christian education over the centuries often involved a catechism, decade after decade, where both the student and teacher memorized a long and complete set of doctrines, often in question and answer format.
Today, it seems that Sunday School teachers are expected to use a book-- even magazine-- that provides new material each and every week. [Insert link to such publishers.] The teacher is as new to the material as are the students, even if it involves eternal truths.
When, historically speaking, did such publishing industries arise? (Bonus points: have any prominent theologians commented on such a trend in Christian education publishing?)