Ron Stevens Amy Soller Melanie Cooper Marcia Sprang Modeling the Development of Problem Solving Skills in Chemistry with a Web-Based Tutor. 580-591 http://dx.doi.org/10.1007/978-3-540-30139-4_55 2004 conf/its/2004 Intelligent Tutoring Systems db/conf/its/its2004.html#StevensSCS04