In a social-media post, he said that although the Education Bureau has condemned and warned a group of secondary teachers of their misconduct and unprofessionalism during last year's violent anti-extradition protests, the authorities have neither identified the teacher and school, nor have they given the reasons for its warning.

Leung said the bureau should enhance transparency in handling complaints against teachers, and prevent innocent students from being exposed to poisonous thoughts, such as separatism, on campuses.

Lawrence Tang Fei, principal of Hong Kong's Heung To Secondary School (Tseung Kwan O), said the local education authorities should spell out clear guidelines for schools and teachers to follow concerning pro-independence or related unruly behavior.

He said that even as a school principal himself, he's not informed as to how teachers had breached their code of conduct last year.

Tang urged the authorities to compile a casebook, detailing the out-of-line behavior and the penalty a teacher involved should get. "This could provide effective guidelines for schools, as well as teachers, to uphold their professional standards," he said.

Willy Fu Kin-chi, vice-chairman of the Hong Kong Legal Exchange Foundation, warned youngsters that being young does not mean they can escape the long arm of the law.

"Everyone is equal before the law. No matter how old you are, any person who breaks the law must bear the legal consequences," he said.