班主任就是容嬷嬷的孩儿
[bān zhŭ rèn jiù shì róng mā mā de hái ér]
'The head teacher is the child of Auntie Rong (a strict disciplinarian from a Chinese drama).' This metaphor illustrates that just as Auntie Rong is known for severe rules and harsh treatment in Chinese classic palace dramas, the homeroom teacher behaves similarly strict to students in daily school life.