Having just read all of the songs on the recommended list, to make up an annotated singers' songbook for use with kids, I think I know why most of them aren't taught in schools any more-- a variety of converging reasons:

1. Some are hymns. Not in schools, nowadays.
2. Some are VERY non-PC. Schools have not figured out how or when to teach the history that makes sense out of what used to be unquestioned culture.
3. Some are considered too juvenile for elementary age-- you get these at home or in preschool.
4. Some are considered ubiquitous-- doesn't EVERY child know Twinkle Twinkle, so why teach it?
5. Some are considered outmoded-- Daisy would ride a bike now not because a carriage can't be afforded, but because the SUV is still on the wish list.
6. Barney has replaced working-class archtypes (media and classism converging).
7. Classism-- schools hold up middle class values, not crawdads and shortnin' bread. That's po' folks food. Head Start is supposed to end all that and save our children into the middle class. And spirituals? Slave history has historically been a period many African Americans would prefer not to be associated with.
8. Take Me Out to the Ballgame-- yeah, let's DO ditch school today! I don't care if I EVER get back! What school is going to teach that?
9. That still leaves a few songs not accounted for. I guess the catchall answer is, times change.

So I think there is a need for us to pass these songs along, with all the wonderful lore we have about them, and with any wisdom we may have accumulated about what they mean and how they relate to our culture now.

~Susan