Hundreds of thousands of teachers in England and Wales are planning not to go to school on Thursday because they voted to strike.
A strike is when a group of workers agree to stop working to protest against something they think is unfair.
The teachers are angry because the government wants to make changes to their pensions, which they say will leave them worse off.
But the government says it's fair to ask teachers to pay a bit more.
They say their pensions should be more equal to what some workers in other jobs pay.
How will it affect YOU?
Even if teachers are striking at your school, it doesn't mean it's definitely closed for the day.
Some schools will be closed completely, other schools will be open but you won't have as many lessons as normal, and at some schools it will be business as usual.
If the strike does go ahead as planned, it will only affect England and Wales.
What the PM says
The Prime Minister David Cameron doesn't want teachers to strike and today he'll ask them to think about changing their minds.
The government says the strike will be bad for kids' education because they'll miss out on lessons.
What is a pension?
A pension is a pot of money you add to over your lifetime so you have enough money to live on when you're older and you retire, or stop working.
The government gives everybody in the UK a pension when they retire, but the amount you get each month depends on how much you've put in.
Some people have their own personal pensions too, so they have more money when they stop working.