It IS reading music.
Shape Note music uses the same staff, scales, key signatures, notation, and other symbols as standard music, with the exception that the body of the note is not always an oval (round) shape. It could be (in Walker's 7-shape system) a tiny trapezoid, crescent, diamond, flag, oval, square, or a triangle.
Anyone who can read "regular" music can read shape notes, it's just that for a-Capella 4-part singing, it's faster and easier for children and other beginner or untrained singers to match the pitch to the shape. Once you get the "DO" you can get all the intervals right and sing every part on the page, no matter what the key signature.