@inproceedings{RickBejanRocheetal.2012,
  author    = {Jochen Rick and Alexander Bejan and Christian Roche and Armin Weinberger},
  title     = {Proportion: Learning Proportional Reasoning Together},
  series = {21st Century Learning for 21st Century Skills : 7th European Conference of Technology Enhanced Learning, EC-TEL 2012, Saarbr{\"u}cken, Germany, September 18-21, 2012. Proceedings},
  publisher = {Springer},
  address   = {Berlin},
  isbn      = {978-3-642-33263-0},
  doi       = {10.1007/978-3-642-33263-0\_52},
  pages     = {513 -- 518},
  year      = {2012},
  language  = {en}
}