I've sung in scholas that accomplished the Introits, Offertories, and Communions with solid competence, fitting for the Holy Mass. And yet, when it comes to the Graduals and Alleluias, a different assessment is required. To put it bluntly, they are often botched, and sometimes horribly. This is not surprising. As the most glorious treasures of the repertoire, these pieces can be far more difficult. Indeed, they require a level of mastery that we just don't have yet, not in the early stages of the revival of chant. We will need a few more years before we are prepared to sing these the way they should be sung, week after week.
For this reason, many scholas resort to the Psalm tone versions that are widely available. This is somehow tragic because these chants are the oldest and most beautiful of the repertoire. My goodness, we are talking about Psalms here, the first Christian song, the very musical link to our deepest heritage. There is something strange about doing the correct proper chants for other propers and then singing a disappointing tone on the Psalm itself!
So what is the work around? In the 1920s, Solesmes saw the need and produced the most useful and most overlooked book of this generation. It was called Chants Abrégés. It came out only in French but of course the music itself is the same all over the world.
What they did, and wisely, was reduce the Graduals, Tracts, and Alleluias to the level of difficulty along the lines of the Introit or Communio, so they are approachable. This makes this book invaluable for scholas without decades of experience. It includes chants for the entire liturgical year. The original is in French, as are the titles, but the index is complete so you can easily find the chant you need to sing. The typeface is flawless.
This book should be in every schola's bag of tricks.
You can download the book and print it a page at a time, or just get the print edition for the schola to have on hand right in the choir loft. I strongly recommend this book for parishes using the Graduals for the ordinary form and especially for Extraordinary Form parishes.
