Structure in the Classroom

I believe structure in the classroom is important for students to feel safe and secure. In my opinion, the beginning and the end of class should have the same routine every day. 
If I get the chance to be an elementary school general music teacher, I want to begin my class with a “Hello” song. If I taught a fifth grade choir or became a choral director, I would begin class with a warm-up routine. This way, every student would know it was time for class to begin. 
When I was in high school, my choir director started the class off every day with attendance, then about ten minutes of announcements. By the time rehearsal began, he had already lost his students. I want to have my students begin with music. Always. A “Hello” song, warm-ups, listening exercises… something that involves music to get the class started. I want to learn from this and try to diminish the amount of time spent talking. 
After the beginning of class routine, the next part of rehearsal is determined by how the group sounds. I would keep the rehearsal momentum moving, but how the rehearsal moves depends on what needs to be worked on. 
At the end of the class period, if I were an elementary school teacher, I would end with a “Goodbye” song. Above that age level, I would try to come up with a short routine for the end of rehearsal that is similar to the “Goodbye” song. Now, every student knows it was time for class to end.
Keeping this structure gives students a sense of security because they know what to expect. They will then have the room to grow as musicians and people.