Music history is one of the least loved subjects among most people who choose to study music. In general, history is considered very boring, as most people feel extremely drained listening to the long lectures about what people did in the past. They often think "when I am going to become a composer or a musician myself, why should I care about what some other people did long ago?" Thus, it is very difficult to make students feel interested, or take music history more seriously. Indeed, if it was an optional subject, not many students would have chosen to learn it.
Thus, you need to be very creative here, so that you can make students see the benefit of you Teaching Music History. As you are Teaching Music History, you must see to it that the classes are interactive, and are fun. People get very tired when they have to listen to long lectures without anything to do except scribble notes. If you keep asking them questions, or ask them their opinions, they will pay more attention.
You can also include some fun activities. Try to bring older forms of musical instruments, or old pieces of music. Ask your students to prepare an assignment where they will have to play any piece of their choice, but in the way the people of a certain period played it. This will get their creative minds working, and they can understand better how music has evolved. It will help them in the long run, as they mull over various innovative ways to make their music more interesting.
You can also get them to relate the older forms of music to their daily life. As you are Teaching Music History, you can pause at a certain period, and then ask your students if they knew what their grandparents used to love listening to when they were children. This will help them get closer to their family members as well.