@article{,
  author	= {{M.J.} Behr and I. Wachsmuth and T. Post},
  title		= {{Rational number learning aids: Transfer from continuous models to discrete models}},
  journal	= {Focus on Learning Problems in Mathematics},
  volume	= {20(1)},
  note		= {(selected retrospective reprint from Focus 10(4)},
  pages		= {63-81},
  year		= {1998}
}