绛帐授徒 (絳帳授徒) jiàng zhàng shòu tú

jiàng zhàng shòu tú set phrase to teach students from behind a crimson curtain
Domain: Idiom 成语
Notes: After a story about 马融 Ma Rong of the Han dyasty, who liked to teach from behind a curtain (Guoyu '絳帳授徒')