Opera. In First grade. Really?
The most fun a music teacher can have is a classroom full of students sight reading for 30 minutes. (I'm allowing for a little dancing and conversation to get the full 45 minutes in of course.)
So teaching how to read music is the #1 challenge.
I started in PreK & Kindergarten giving brief board exercises on note values and clef signs. Then in First grade it's off to the races. Generally speaking, their heads don't go down until January, but getting them acquainted with the tool of sheet music and the idea that you can learn to see the graphic representation of what we sing is something that has to be repeated in every class.
We had a policy of "no homework", "no tests" so, repetition was vital.
Typically, for example, we would begin the year with "Wade in the Water". It's fun to sing and a descant line is a nice way to show part singing. Then some Gershwin like "'SWonderful", or, "They Can't Take That Away From Me". One our favorites was Jerome Kern's "Stouthearted Men".
So, along with several easy jazz classics, I would introduce them to great composers and the finest vocalists through what they always would call "Opera". I'd explain it's just a melody and words, don't get hung up on genres. And since First graders can't read English so well why not some German, or Italian?
Here's a list of some of the songs (the titles are links to free sheet music):