"Teaching is one of the most vocally demanding professions. In addition to long periods of speaking, there is often environmental noise competing with your voice for the students’ attention, inadequate ventilation, few opportunities for resting the voice, and extra vocal burdens such as tutoring, lunchroom monitoring, and parent-teacher conferences."
As music specialists or art specialist we don't generally have to worry about lunchroom or SEP's, we still have performances and other activities that we use our voices for. Read up on the tips from the website. Some are very specific to teachers.
Here are some teacher specific tips:
Use personal microphones. These devices aren’t very expensive and will help your voice carry to the back of the classroom. Using a microphone may help prevent trauma to the vocal fold (also known as vocal cord) mucosa by reducing the need to speak loudly and forcefully.
Warm up your voice before teaching. Just as a singer or actor warms up their voice before a performance to maintain a healthy voice, the teacher should similarly get his or her voice ready for the classroom “performance” demands. .
Balance the vocal demands of teaching with vocal rest. You would not expect yourself to be able to participate in a sport every day without some rest periods in between. So too, your voice production system needs rest. If possible, schedule one to two hours of complete voice rest after you finish teaching for the day, and limit extraneous voice use on those days when your voice is feeling particularly tired.
Quiet the class environment as much as possible. Speaking against background noise is quite difficult, and puts a significant added strain on your voice production system. Get together with other teachers in your school to brainstorm ideas for managing environmental noise.
Enlist student participation as much as possible. Class participation is dependent upon the age of the students, among other factors, but it can help to have a discussion with the class about your voice problem. Explain that you cannot shout. Tell students that talking amongst themselves while you are teaching is not only distracting to other students, it’s hard on your voice.
Use non-vocal signals to gain attention of the students. Flashing room lights, clapping hands, or ringing a bell are easy alternatives to yelling for attention. Sometimes even standing quietly is enough to get a few of the students’ attention and then those students will quiet the rest of the class.
Move about the room to avoid rigid posture. Standing in one place for the whole class encourages stiffness, which is counterproductive to healthy voice production. Movement helps keep the muscle of the throat and upper body relaxed.
You can also read about specific vocal warm-ups on this website. I prefer to sing in the car on the way to work. Whatever you do, get your voice warm and working before you see your kids.
Hope this info helps!