Pupils will soon be able to get free sanitary products in all primary schools in England, Wales and Scotland.
The government says the change will happen in England from 2020.
Campaigners argued that some girls find themselves missing school because they cannot afford to buy the items.
In March 2019, UK Chancellor Philip Hammond, who's in charge of how the government spends the country's money, at first announced that the products would be offered to all secondary schools and colleges in England.
But many people said the plan should include primary schools too - and now that is happening.
What about the rest of the UK?
In 2018, the Scottish government said it would pay for free sanitary products to be available in all schools.
In April 2019, the Welsh government also announced that primary and secondary pupils across Wales would be given access to free sanitary products.
Northern Ireland hasn't made any announcements about helping to pay for items to be given free in schools - the Northern Ireland government isn't sitting at the moment - but one local authority offers them in some public buildings.
What are sanitary products?
They are products that girls wear during their period. You'll see them in any supermarket, but they can cost a lot of money.
Periods are a normal part of growing up for girls and usually start with puberty, but campaigners say that girls who can't afford sanitary products are embarrassed to talk about it and it can lead to them missing lessons.
The Girl Guides have campaigned about period poverty for several years and say their research suggests that 1 in 3 11 to 21-year-old girls and young women have missed school or college because of their period.
The Department for Education said that it would begin talking to school leaders about how to manage this plan from early next year.