You've seen those large exercise balls at the gym but now they're rolling into the classroom, where a Fort Collins teacher is using the balls to improve her students' concentration and posture.About a month ago Tiffany Miller replaced the desk chairs in her fourth-grade classroom with stability balls, and now she's seeing improvements in behavior and learning."We know with brain based research that when you are actively sitting your brain is more engaged. The other reason is the posture is better, which means that there is more blood flow going to your brain," said Miller, a teacher at Bauder Elementary.By using core muscles to balance on the balls, the students stay focused, which improves learning and posture."I've never thought about going back to a chair," said student Nolan Diana."It helps me learn," another student said."When you had chairs you were always slouching. But if you slouch on a stability ball you will fall over," explained student Madelyn Cesa."If you don't have good posture when you are older you are just going to be like this, hunched over," Nolan said, bending over.The stability balls allow the students to move around, minimizing restlessness."I am a huge fan of being able to fidget," Miller said.Her students agree."They are better than chairs because you can wiggle around and in chairs you just stay really stiff," said Madelyn."I have noticed a change. I think if you asked the kids, they'll tell you they've noticed a change They enjoy sitting in their seats now," Miller said. "I don't know if it would work for other teachers, but it works for me."The only problem is if you leave your seat, it might just roll away.The stability balls were purchased thanks to a grant from the Medical Center of the Rockies. The total cost of the balls was $400.