The culling of key phrases from a history textbook and a push to instil Chinese national identity in students has raised fresh concerns that education in Hong Kong is under pressure from Beijing, as it seeks to stamp out any hint of pro-independence sentiment.
Student-led protests demanding democratic reform for semi-autonomous Hong Kong and the emergence of an independence movement have posed an unprecedented challenge to Chinese authorities in recent years.
To quell youth rebellion, officials on both sides of the border are emphasising the need for students in the city to learn more about mainland history and to understand Hong Kong in a national context.
But critics accuse the government and Beijing of "brainwashing".
The blacklisting last month of commonly used terms in a school textbook raised questions about whether history was being rewritten altogether.
"Our concern is about whether there is direct interference or if there is any self-censorship involved," Ip Kin-yuen, lawmaker for the education sector and a democracy advocate, told AFP.
A review panel reporting to the education bureau rejected as "inappropriate wording" phrases referring to Hong Kong's colonial past in a history textbook that had been submitted to them for approval before publication, according to documents leaked to local media.
The offending terms included "The transfer of Hong Kong's sovereignty to mainland China" and "China recovered Hong Kong".
Questioned about the amendments, education secretary Kevin Yeung told lawmakers China had never given up sovereignty of Hong Kong.
Some pro-democracy figures accused him of doing Beijing's bidding and erasing Hong Kong's past.
China ceded Hong Kong to the British when the first Opium War ended in 1842. After more than 100 years of colonial rule, Britain returned the territory to China in 1997.
Schoolbooks must be passed by a review panel to gain inclusion on the government's recommended reading list.
Panel membership is confidential but includes teachers, academics and staff from the education bureau, which has defended the review system as a fair "professional" process.
But one industry executive, who did not want to be named, said publishers had discussed the need for more transparency on acceptable phrasing after the textbook incident and had suggested the government share a glossary of terms "to avoid misunderstandings".
Concerns about Beijing's influence on Hong Kong's book industry were fuelled after a recent investigation by local channel RTHK discovered China's liaison office indirectly owned more than half the city's bookshops.
Earlier attempts to introduce a patriotic "national education" curriculum into Hong Kong schools galvanised tens of thousands to take to the streets in 2012, forcing it to be shelved.
However, the push to instil a sense of Chinese national identity is now regaining prominence in government rhetoric.
In her first policy address last year, city leader Carrie Lam announced that Chinese history would be taught as a compulsory subject at junior secondary level from the end of 2018.
This would help students become knowledgeable and responsible citizens "with a sense of our national identity, and contribute to our country and our society", she said.
A new draft of the Chinese history curriculum released last month puts Hong Kong's past within a national context, an approach the education bureau said was "natural, reasonable and logical" and supported by teachers, in a statement to AFP.
But democracy campaigner Joshua Wong told AFP he believed the government was using "subtler ways to promote their brainwashing education".
Wong led the 2012 education protests as a 15-year-old school pupil.
Pro-establishment politicians have also taken aim at liberal studies, a mandatory subject for senior secondary school pupils which covers political topics and has been blamed for stoking anti-government sentiment.
The government last month denied a report it would downgrade the subject to optional.
Liberal studies teacher Tong Kam-fai, who works in a Roman Catholic secondary school, said blaming it for unrest was "very unfair".
"Critical thinking is not the same as protest and opposition," he told AFP.
However, Tong said he still felt free to speak to his students about controversial topics, including the crackdown on democracy protesters in Beijing's Tiananmen Square in 1989, discussion of which is heavily suppressed in the mainland.
Lawmaker Ip believes the freedoms at the heart of Hong Kong's education system are still intact.
But he fears the government may become increasingly "politically correct" to reflect the thinking of mainland authorities and continue to blame education for social divisions.
"Young people are frustrated these days for many reasons, it's not out of education," Ip told AFP.
"We want our students to be able to understand the world, not to be indoctrinated."