P. Jermann, A. Soller, and M. Mühlenbrock. Proceedings of the European Conference on Computer-Supported Collaborative Learning (Euro-CSCL 2001), page 324-331. Maastricht, The Netherlands, , (2001)
R. Stevens, A. Soller, M. Cooper, and M. Sprang. Intelligent Tutoring Systems, volume 3220 of Lecture Notes in Computer Science, page 580-591. Springer, (2004)