In phase three, under the influence of such educators as Karl G. Maeser, Joseph M. Tanner, and David O. McKay, the Sunday School established formal teacher training courses. Beginning in 1892 as an experiment at Brigham Young Academy at Provo, Utah, these classes were soon part of every ward’s Sabbath schedule. Innovative leaders in the 1890s also published comprehensive officers handbooks and conducted stake and general Sunday School conferences and model Sunday Schools. Stake boards were established soon after 1900 to help train local workers. By 1915 the Sunday School offered its own specially written teacher trainer manuals and was educating teachers for other auxiliaries and priesthood quorums.

The early twentieth century revealed other indications of the Sunday School’s determination to make its teaching effective. Having previously moved from the one-room school to the graded class, the Sunday School now refined its grades, added kindergartens, instigated annual promotions, and embraced adult education. The Parents Class, designed to help parents fulfill teaching responsibilities in the home, first succeeded in the Ogden Utah Weber Stake (formerly Weber Stake) and was later authorized for Sunday Schools in 1906. Another important landmark was the development, a decade later, of a 16-year-long curriculum in Church scripture and history, with lesson textbooks replacing outlines.