Mann, Ralph. An Examination of High School Failures as Revealed in the Literature of the Subject in Order to Determine the Nature, Extent, Causes and Remedies, thesis, 1950; (https://digital.library.unt.edu/ark:/67531/metadc130213/m1/31/: accessed October 20, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .