My students are to sit and read quietly or rest their heads on their desks. I have to be in the hall for hall duty, so I have another student (a well-respected, leader-type) dismiss students. They must be called one at a time when their bus is announced. Anyone who was talking or playing will be called last and may have to stay in the classroom a few extra seconds before being dismissed. This generally works very very well and the kids enjoy it. It's also no work for me.