One resource I’ve used is The Story of Christian Music by Andrew Wilson-Dixon.
It’s basically an overview of major Christian traditions of worship. from Gregorian chant to the present.
It does well in helping students understand the context and traditions from which the variety of hymns in a typical hymnal have been birthed.
An Anabaptist Resource for Teaching and Learning
The Dock is conceived to serve schools in the spirit of Christopher Dock, the devoted teacher who authored a warmly practical teacher's manual in colonial America. Read more...