Eighth graders

Just as I'd feared. Eighth graders still have some growing up to do. Some of them anyway. After not having 6,7,8 graders for two years, this year I changed routes and now have 8th graders. I can't get them to stay in the bus after they board. They want to stick their head, arm, voice out the window to impress their classmates. I have had it out with them over this for about a month now. I have assigned seats, had them close windows on hot days, yelled at them, tried to reason with them, all to no avail. I will write them up if I have to but would rather not. I would rather handle behavioral problems myself. I could have them write sentences like the elementary students are required to do. I would rather not do that either. I just want them to grow up a little bit and keep their hormones in check in the mean time. Is that too much to ask?