I have some kiddos who like to tip their chair. I was a young boy once, and I actually tipped my chair some myself. I still do, from time to time, as an adult. When I was younger I actually tipped back and hit my head, gashing my head open. It probably seemed worse than it was, but I still tell people that I split my head open.
Where am I going? Right, chairs in class! So I have given reminders upon reminders about 6 legs on the floor, four for the chair and two for you. But that got tiresome. Following the idea that the punishment should fit the crime, I decided that you'd lose your chair if you tipped your chair after being warned (got all that?).
I took a chair away yesterday at 1:30, and then had to do it again this morning... at 9:06am. No problems thereafter. After the first 2-3 times of him asking, he stopped asking and was on his knees by his desk, or working under his desk. We'll see what tomorrow brings. Hopefully he keeps his chair.