5Johnson, D. W., Johnson, R. T.Stanne, M. B. (2003). Cooperative Learning Methods: A Meta-Analysis. http: //www. clcrc, com.
6Johnson, D. W. ,Johnson, R. T. , & Holubec,E. J. (1993). Circles of Learning : Cooperation in the Classroom, (4th ed. ) Edina, Minn: Interaction Book Co. ,17.
7Slavin,R. E. (1990). Cooperative Learning:Theory,Research and Practice, Boston, MA : Allyn and Bacon,34.