Hiroyuki Sakuma. Children's Multiage Grouping and the Teacher Training in the Jena-Plan: A Case Study of GJP's "Diplomkurs" in Germany. Annual Report of the Center for Teacher Education Research, Tamagawa University. 2015. 5. 19-29
Hiroyuki Sakuma. Peter F. Drucker's Early Thoughts on Totalitarianism: Focused on his Documents and Works in Frankfurt between 1929 and 1933. Bulletin of College of Education Tamagawa University. 2015. 55-71
Hiroyuki Sakuma. Petersen's Understanding of Pestalozzi: Centering on the Idea of "Menschenschule". Research on Education of Man: Bulletin of Japan Society for the Study of Pestalozzi and Froebel. 2015. 27. 27-51