Here are a few quick ideas that we've found useful in the past, but you're the experts. Let us know what's worked in your music classroom.
1. Student-designed curriculum: One sure-fire way to get your students engaged is by letting them have some control over what they're learning. Let them vote on what song to learn next. No one likes to be told what to do without reason, so take some time to explain why you're teaching certain ideas or certain techniques and open up the dialogue to include your students. You'd be surprised how effective this kind of "real talk" can be, particularly in the music classroom.
2. Taking a deep breath is always a good idea, but even more so in the music classroom where many instruments require breath control. Deep breathing can reduce stress before a test and making an absurd noise together can be a great icebreaker at the start of a class. As a teacher, I suggest going first and letting the students laugh at you. They aren't laughing at each other, they're relaxed, and laughter is always a great energizer. Any activity that gets your students moving around the room keeps the group energy up.
3. Go online: Switching mediums can be a great way to redirect your students' attention. It might initially seem difficult to take a music classroom (full of instruments) online, but check out these games for grades 1-5. Also, check out Chromatik's own posts here and here about different ways to integrate technology into your music classroom. Students are already living their lives online. Why not put their music front and center?
4. Create a Musician Family Tree: Music history can be one of the harder subjects to teach in a music classroom, mostly because students don't understand how music has developed over the years. Have students pick a modern current musician and then trace his or her style back through time, creating something of a musician family tree. Students will then be able to better visualize how genres have evolved and influenced one another.
Music is dynamic. Why shouldn't your classroom be as well?