US Department of Education, Washington, DC (2009), http://eric.ed.gov/?id=ED505824 Ziebarth, S., Malzahn, N., Hoppe, H.U.: Matchballs – A multi-agent-system for ontology-based collaborative learning games. In: Herskovic, V., Hoppe, H.U., Jansen, M., Ziegler, J. (eds.) ...