Thousands of students took part in a third 'strike' demanding action on climate change - evening bringing one of London's busies streets to a standstill.
Hundreds of students marched past Downing Street where they chanted “Theresa May, hear us say, climate change is here to stay”.
The march began at Parliament Square where organisers led chants, including “We want, we want, justice” in the style of Queen song We Will Rock You.
As cars were brought to a halt to wait for the march to pass the students chanted “engines off”.
A sit-down saw Oxford Street and surrounding roads brought to a standstill, and while police moved most of the protesters away, a defiant group stayed on, to the annoyance of some road users.
One protester was taken into a police van after refusing to move from the road, but the Metropolitan Police said there had been no arrests.
Organiser Cyrus Jarvis, 16, a year 11 student from London Academy school in Barnet, North London, said: “The police tried to frighten us with arrests but we just moved on.
“We are really sorry for anyone who did have issues because of us, but unfortunately this is what we have to do to get our point across to the Government.
“If we don’t cause disruption they don’t listen to us and they haven’t listened to us in the past.”
Francesca Peduti, 17, from Bedford, said: “Our future won’t exist if our Government won’t find a way to combat climate change. This needs to change.
“I have a two-year-old sister. I want her to grow up in an Earth that is safe.”
Similar events took place across the country, with schoolchildren in Cambridge schoolchildren taking part in a 'die-in' to raise their concerns.
In Canterbury in Kent, students lay on the floor holding pictures of endangered and extinct animals.
Sixth-former Nova Levy-Rapoport, 17, an organiser for the UK Student Climate Network, said: “There is so little time that we have left before we enter such a volatile future and if I was not here today it would be a literal betrayal to myself, my family, my friends and my future.”
Those going on strike are demanding that the Government declares a state of climate emergency, and reforms the curriculum “to address climate change as an educational priority”.
They are also campaigning for the voices of young people to be considered when it comes to policy-making and for the voting age to be lowered to 16.
The strikes come in the wake of a UN report which warned that limiting global temperature rises to 1.5C above pre-industrial levels, beyond which climate impacts become increasingly severe, requires unprecedented action.
That includes cutting global carbon dioxide emissions by almost half within 12 years.
Environment Secretary Michael Gove has previously spoken of his support for the strikes, saying: “Collective action of the kind you’re championing can make a difference, and a profound one.”