Also because each school visit may take some preparation, making more than four visits may not be possible for really busy astronomers. Visit the same classroom over time. Go for depth rather than exposure. We know that teachers who see more than one class each day ideally want to expose all of their students to the astronomer. Although you will initially involve a smaller group of students, these students will benefit much more from the astronomer's multiple visits and personal contact.
Teachers can use the new skills they develop to enhance astronomy with other classes.
If all partners agree, you can add additional students after you have been working together for a while. Consider this a pilot project which can be expanded for future years. The teacher should be responsible for student discipline and classroom management. Visiting astronomers, as volunteers in the classroom, should not be expected to manage student behavior in the classroom. Rather, teachers should stay actively involved in the classroom, both to model learning and curiosity to students and to assist the astronomer with any discipline or logistics.