At midday, Canberra students will join tens of thousands across Australia and the world in the second School Strike 4 Climate march, after protests around the country made headlines last November.

In striking, they defied the orders of Prime Minister Scott Morrison, who has called for less activism and more learning in schools, and stepped into a storm of criticism led by some Coalition MPs.

But, four months on, students are expecting an even bigger turn out at more than 50 Australian rallies, including up to 2000 students at the Canberra event in Garema Place.

On the eve of the strike, Ms Berry said the ACT government, which plans to switch the territory to 100 per cent renewable energy by next year, strongly believed in student agency and supported their right to take action.

"This issue is clearly something that students and young people are passionate about, as we all should be," she said.

"Participation in activism such as the climate strike is a learning experience in itself. School and education doesn’t just happen in the classroom."

NSW Labor leader Michael Daley has also thrown his support behind the strike as a demonstration of young leadership and the democratic right to protest.

But Premier Gladys Berejiklian has slammed his position as "appalling", warning it is inappropriate for a politician to encourage children to miss school for any reason.

Busy making signs ahead of the strike, 14-year-old Maanha Manzur from Harrison School said she was tired of excuses from leaders. The strike last year drew attention, but this time, she said, they wanted action.

"We want to stop Adani's [Carmichael] coal mine, we want an end to new fossil fuels, and 100 per cent renewable energy by 2030 [Australia-wide]," she said.

Almost every year of her life has now ranked among the 20 hottest on record but Maaha said she learnt little about the science and speed of global warming at school.

"It's the greatest threat to our generation but no one talks about it," she said.

"We don't want our futures to have a question mark."

One of about 15 teenage organisers of the ACT strike, Maanha will walk out of school at 10am on Friday.

She brushed off cynicism about who was behind the protests ("Us!") and calls to keep politics out of schools, saying it was education that had motivated students to act in the first place.

"We've connected the climate dots now," she said.

At Mary Mackillop College, 15-year-old Olivia Boddington said it was terrifying that she and her younger sisters would not get a say in their future until it was too late.

Olivia only heard about the first strike as it lit up news bulletins that evening in November but said this time ACT schools were supporting kids wanting to get involved.

"Some of the younger kids are particularly passionate," she said.

More than 800 academics and a number of unions including the Australian Education Union have also backed the strike.

The ACT education directorate confirmed students would not be penalised or stopped from attending the rally, but stressed they would still need approval from their parents or carers and encouraged parental supervision during the protest. The directorate had not been told of any issues or concerns during the last strike, a spokeswoman said.

While posters have been displayed across schools by students in the lead-up to the strike, it is understood teachers have been advised not to actively encourage strikers.

"But schools have been so supportive," Maanha said. "Especially my science teacher."

The global school strike movement was inspired by 16-year-old Swedish student Greta Thunberg who began camping out the front of her own country's parliament each Friday to demand climate change action in September. Greta continues to strike regularly and says her grades are still strong.