The Book of Han, the official history of the Former Han dynasty and the second of imperial China's standard dynastic histories, was begun by Ban Biao and continued by his son Ban Gu, who was imprisoned and died in 92 CE with the work still unfinished, its treatises on astronomy, chronology and genealogical tables in particular left incomplete. Emperor He turned to Ban Gu's sister, Ban Zhao, to complete it, summoning her to the imperial library specifically for that purpose. Completing a dynastic history's technical tables required exactly the kind of specialized scholarly training, in astronomy and calendrical calculation as well as classical literature, that Ban Zhao had received within her family's scholarly household, and her work brought the Book of Han to the finished form that later Chinese historiography treated as the template for how a dynasty's official history should be written.
Her standing at court extended well beyond textual scholarship. Emperor He appointed her tutor to the women of the imperial harem and the ladies in waiting, who addressed her by the honorific Cao Dagu, drawing on her husband's surname Cao and a term of respect for an accomplished woman. Among her students was Deng Sui, a young woman she taught history, the classics and astronomy, who later became Empress Dowager Deng and, once installed as regent for a child emperor, is recorded as having consulted Ban Zhao directly on matters of court policy, giving a woman formally credentialed only as a tutor and historian a documented voice in Eastern Han political affairs.