2Sharan, S. & A. Shaulov. 1990. "Cooperative Learning, Motivation to Learning, and Academic Achievement". In S. Sharan (Ed.). Cooperative Learning: Theory and Research. Praeger Publishers.
3Johnson, D. W. & P,. T. Johnson, 1994. Learning Together and Alone: Cooperative Competitive, and Individuolistic Learning. (4th ed.). Allyn and Bacon.
4Thomas, L. G. & E. B. Jere. 2002. Looking in Classrooms (8th ed.). Prentice, Hall, Inc. China Light Industry Press.
