Have you ever had backache? It might sound like something more likely to affect your grandparents, but about one in 10 kids has back problems.
Experts reckon one of the reasons for stiff backs are badly designed desks and chairs in your classrooms.
Maddy's been to check out one school that's made some big changes...
"If your shoulders ever feel heavy, or your neck is sore, it could be because there's a problem with your back.
Experts say back pain is often caused by slouching at your desk. It might feel more relaxing than sitting up straight, but it's actually putting a strain on your spine, which is the group of small bones that run down your back.
If you keep doing this when you're young, it can cause loads of problems when you grow up.
I definitely slouch too much so I was really excited to check out the furniture that some schools have started using to try to help kids sit properly!
You can adjust the tables so they are higher or lower, and you can tilt them upwards so you don't have to lean down to write on them.
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The stools can also be made taller or smaller. The trick is to match the pointy bit at the front, with the back of your knee. If they are the same height it is much more comfortable.
All this means that whatever size you are, you can sit in a position that's perfect!
It does feel a bit weird without a backrest, but you soon get used to it. I'm short for an adult and it felt amazing to sit a desk that fitted me exactly. I wanted to try to sneak it into the Newsround car!
Pupils at the primary school I visited in Essex, in south east England, say they feel much better since they started using this kind of furniture a year ago.
I could definitely tell they were all sitting up very straight. Much better than most of us in the Newsround office!
To make extra sure everyone's backs are in tip top condition, kids also have to do daily exercises to stretch their muscles. For example, leaning from side to side, rotating their hips in a circle and giving their hands a good old shake!
I felt a bit silly joining in, but it was actually really good fun!
Experts are studying children at the school to help them decide whether other places should get the same kind of furniture.
It is expensive to buy, but they say it is worth the money to stop kids having sore backs both now and in the future."