Hundreds of schools in the UK and 120 other countries have been taught the same lesson at the same time, across two time zones.
The aim was to raise awareness about the millions of children who don't get the chance to have an education.
Press Packer Dev's school took part in this special event. Here's his story.
"My school took part in a special event to break the record for the world's biggest lesson. At the same time we learnt about how some kids around the world don't get an education.
Sat on mats
We had the lesson outside on the grass, right next to the Houses of Parliament in London.
We did this because lots of kids in Africa have their lessons outside.
We had a blackboard and mats to sit on. The only problem was that it was raining!
We got drenched and it was very cold, but we stayed because it was important.
Speaking up
In the lesson an MP talked to us about what causes children not to have an education, including war and poverty.
We learnt that if everyone speaks up together then things can happen.
Government pressure
I think it's important that children all around the world get an education and we need to pressurise the government and local MPs to help this happen.
It was really interesting taking part in this unique lesson - even if it did rain!"
Dev, 12, London
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