About 8,000 students and teachers took part in a citywide class boycott yesterday to demand the scrapping of the national education curriculum.
Participants attributed the higher-than-expected turnout to Chief Executive Leung Chun-ying's weak response to the issue.
He announced on Saturday that he would let schools decide whether to teach the controversial subject instead of making it mandatory.
But protesters said "threats of indoctrination" still remained because the government could force schools to implement the policy through measures such as subsidy requirements.
At Chinese University in Sha Tin, where a rally was held, associate professor of sociology Chan Kin-man cut short his three-hour lesson and told his 100 students they could join the boycott, which started in the afternoon. About a fifth of them walked out and Chan promised to hold catch-up classes.
The professor said the high turnout at the demonstration held at Chinese University Mall was a sign of public discontent and distrust in the government. Fellow Chinese University professor Ma Kit-wai stood on a makeshift stage in front of the sea of black-clad protesters, some holding umbrellas in the sweltering heat, and denounced national education for promoting "old-fashioned values".
He said: "It is just outdated to [force] people to do something just because you are Chinese."
The crowd sang songs and chanted. Two banners on the stage read "anti-national education, anti-colonialism, class boycott by university students".
Organisers, who had initially expected 1,000 participants, said 15 universities and tertiary institutions took part in the rally, including lecturers from the mainland and Taiwan.
Lo Shih-hung, from National Chung Cheng University in Taiwan, said the island had gone through the same "brainwashing by the party state" and national education should be scrapped.
Jack Qiu, from Hubei who teaches journalism at Chinese University, said the recent turmoil had raised debate among mainland intellectuals over the need for political education in mainland schools.
Some protesters also descended on the government headquarters in Admiralty, the site of a massive nine-day demonstration that led to Leung's climbdown.
But defending his decision yesterday, the chief executive urged protesters not to "live in the past" or bear grudges.
He said he did not completely withdraw the subject as some schools would like to teach it. A committee, led by Executive Councillor Anna Wu Hung-yuk, set up to scrutinise the curriculum held its second preparatory meeting yesterday.
But some students deemed the boycott unnecessary. "The government has already [backed down]. There is no need for such radical action," said Darren Kwan Chiu-ho, of the University of Science and Technology.
Others opted not to miss lessons at the start of the semester. Classes opened on Monday for most schools.