Wilkens, Hendrianne J. “Textbook Approval Systems and the Program for International Assessment (PISA) Results: A Preliminary Analysis”. IARTEM e-journal 4, no. 2 (February 22, 2012): 63–74. Accessed April 19, 2026. https://mail.iartemejournal.org/index.php/IARTEM/article/view/777.