After the late Heian period, the Oe clan and the Sugawara clan monopolized the position of Jidoku with the hereditary title of Kidendo hakase (chief experts on the history of Japan and China) (Monjo hakase (professor of literature)).
だが、平安時代後期以後、紀伝道博士（文章博士）を世襲した大江氏・菅原氏が侍読の役を独占した。