In. 1923-24 he established Undeb Athrawon Cymreig and was secretary of the Union until the end of World War II when Undeb Cenedlaethol Athrawon Cymru was set up. He was also a member of the editorial board of Yr Athro from its commencement in 1928 until his death. He published very useful textbooks facilitating the teaching of Welsh , namely Llwybr y Gymraeg 1, 2 and 3 and Priffordd y Gymraeg 1, 2 and 3 (both series pre-1930 ) and Cynllun Newydd yn y Gymraeg ( 1930 ), followed by Some Notes of Lessons for Teachers of ‘Priffordd y Gymraeg’ ( 1932 ). He contributed to Yr Athro a number of articles and notes on teaching Welsh and gave lectures in many localities on teaching children Welsh , particularly as a second language. He was the principal lecturer of the Union of Welsh Societies on bilingual teaching in schools, 1929-40 . He received an hon. M.A. of the University of Wales in 1951 in recognition of his valuable contribution to education.

D.O. Roberts was very active in college and eisteddfod circles in Wales , in the National Book Festival , and in the musical life of the Cynon valley . He often gave radio talks drawing particular attention to the minority cultures and languages of Europe . His ideals were internationalist and pacifist and he strongly supported the cause of selfgovernment for Wales .

He m. Ann Edwards 23 Apr. 1917 and they had one son and one daughter. He d. 29 Aug. 1958 .