Martina A. Rau Vincent Aleven Nikol Rummel Intelligent Tutoring Systems with Multiple Representations and Self-Explanation Prompts Support Learning of Fractions. 441-448 2009 AIED http://dx.doi.org/10.3233/978-1-60750-028-5-441 conf/aied/2009 db/conf/aied/aied2009.html#RauAR09