The umbrella organisation, known as the Hong Kong Student Strike Alliance, comprises several secondary school student groups.
It says an estimated 3,000 to 4,000 students from nearly 1,00 schools they plan to join the class boycott from Tuesday, the second day of the new academic year.
They will be joining boycott plans announced earlier by students from 10 tertiary institutions.
The alliance says it’s not leading the class boycott, but hopes students from different schools could decide their own course of action, for example whether to stage an indefinite class boycott at individual schools, or to take a day off every week.
What they do may vary, but their five demands are the same as anti-government protesters – which include the full withdrawal of the extradition bill, universal suffrage and investigate alleged police brutality.
The alliance said students have set September the 13th as the deadline for the government to respond, and they may escalate their campaign if officials fail to do so.
While it does not encourage students to take part in violent protests, it says students may block school entrances and access to public transport.
The education minister, Kevin Yeung, says he’s written to primary and secondary schools, urging principals and teachers to do their jobs and ensure normal teaching will continue.
Mr Yeung said teachers should lead by example as the public has strong expectations for them to be professional and have high moral standards.
He’s also urged schools to pay attention to the emotions of students and teachers, and seek professional help if necessary.
The minister had earlier promised that his bureau won’t collect a list of students and teachers who would join the class boycott, but that officials need to learn about the scale of the action.
He also said that it’s up to individual schools whether to punish students who took part.
On school bullying, the education chief says schools should report teachers found to have bullied students, to see if they’re still fit to keep their jobs.
This follows cases of children of police officers being targeted.