Thousands of students are taking to the streets to demand action on climate change and call on the Government to teach children about the threat it poses.
Organisers say more than 120 protests are taking place in the UK, with tens of thousands of students attending – despite exams taking place in schools around the country.
London, Brighton, Birmingham and Edinburgh’s events are expected to be particularly popular.
In London, students are gathering in Parliament Square before marching on the Department for Education.
The strike calls on ministers to “Teach the Future”, by reforming the curriculum to include more material on climate change.
Shakira Martin, a former president of the National Union of Students, will address the London demonstration.
Similar large-scale youth protests took place in February and March this year, with students “striking” from school to take part.
Extinction Rebellion, which organised protests in London last month, said it is not involved in Friday’s event but supports the cause.
Although the strikes are a “decentralised movement” and have no formal leader, many consider Swedish teenager Greta Thunberg to be the figurehead.
Ms Thunberg began “striking” from school on Fridays to lobby the Swedish parliament on climate change in August 2018.
Her protest sparked similar strikes across Europe, North America and Australia.
Protesters in 110 countries are expected to take part in Friday’s strike.
UK spokesman Jake Woodier, 26, said the Teach the Future campaign is designed to educate students more about climate change in schools.
“Students are really learning and gaining their knowledge from outside of education,” he said.
“We’re calling for dramatic reform of the education system to provide students with the knowledge and tools to be equipped for the changing world which they’re going to be inheriting.”