Well, anonymous Guest, we all have different talents. I learnt the skill of singing with a book in front of me when I was a boy in a church choir. As far as folk-singing in England goes, I think it only a slight exaggeration to say that every non-gentry male singer in rural parts, up until the mid twentieth century, learnt his craft in exactly the same way. From the late nineteenth century onwards, school singing lessons (using books) would have been a starting point for working class children everywhere.
Obviously, there are many other non-literate strands in the fabric but, from the time of Wynken de Worde at least, singing from a song sheet has been a major part of communal singing.