After Century Expanded and Century Oldstyle, Morris F. Benton created this third variation of Century for textbook publishers Ginn & Company who asked ATF to develop a typeface for maximum legibility. “After many studies and eyesight reading factors dating from 1912, Century Schoolbook and Italic were designed in 1917–19 and released in 1918–21. Century Schoolbook Bold was designed in 1919 and cut in 1923.” [McGrew]
It is broader than Century Expanded overall, with less contrast and a pared down italic.