Joshua, 15, convenor of Scholarism and a student at United Christian College (Kowloon East), formed the protest group in June last year to voice student opposition to the proposed "moral and national" education programme for primary and secondary schools. It is due to be introduced in primary schools in September.
He and other Scholarism members joined Sunday's march to protest against the "biased nature" of the new curriculum, and education minister Eddie Ng Hak-kim's plan to "implement first, evaluate later".
Organisers claim 90,000 people marched from Victoria Park to the government's headquarters in Admiralty; police say 32,000 took part.
"I didn't care so much about politics before," Joshua says. "But I became interested in politics and student activism after the high-speed rail-link protest and the five-district referendum movement in 2010. I thought students could fight for social justice. We need to be politically aware, not politically apathetic."
The name, "Scholarism", represents student-related political issues taken up to a more ideological level, he says. "Our main aim is to persuade the government to drop the national education scheme; we collected 20,000 signatures on the street to petition for this," he adds. "Yet we are also concerned with the June 4 incident, activist Li Wangyang's suspicious death, as well as Chief Executive Leung Chun-ying's new government."
The students say the existing liberal studies curriculum covers Chinese culture and heritage, as well as civic education, so the new subject is unnecessary.
"This is one reason why the proposed curriculum, presenting arguably biased ideas, is a waste of HK$500 million of government subsidy," says Frank, 16, a Form Six student at Tuen Mun's Chung Sing Benevolent Society Mrs Aw Boon Haw Secondary School.
In the past two weeks, Scholarism's protests included members following Ng to interviews and other events to argue against his plans.
Members also staged protests outside the Central Government Liaison Office after the July 1 march and joined protesters that halted the Tuen Mun town hall meeting attended by the chief executive on July 2.
Form Four student Agnes says: "We've researched the advantages and disadvantages of a national education, to come up with a proposal that includes a comparison of Hong Kong's proposed policy, and the policies of more democratic countries, such as Australia. We want to clarify exactly what's wrong with the Hong Kong government's proposed plan."
The group, which has more than 23,000 supporters on its Facebook page, first gained public attention when a video of Joshua speaking eloquently about Scholarism's opposition to the scheme surfaced on the internet in May. "That video inspired me to join," Frank says.
Scholarism had 20 members at the start; now it has about 200. "We're from different schools and backgrounds, but are united by our cause - to resist a biased and confusing curriculum," Frank says.
Most of the group's funds come from the members' own pocket money, plus donations from supporters. "One teacher donated a large amount after hearing one of our members was pepper-sprayed at the June 30 rally," Joshua says. "Public support for what we stand for is part of what keeps us going."
Agnes rejects the criticisms of their opponents. "We're not extremists, and don't want to be labelled as radical activists fuelled by teenage angst."
Frank says: "Scholarism has helped increase student awareness, not only of the national education issue, but also of politics and social injustice in general."
To find out more about Scholarism, go to their Facebook Page.