Kieren, Tom; And Others. Fraction Flags: Learning from Children to Help Children Learn. Mathematics Teaching in the Middle School; v2 n1 p14-19 Sep-Oct 1996. 1996Two other approaches I know of also have strong theoretical bases and practical success. One has been developed in the Netherlands by the Researchgroup on mathematics education in Utrecht, and the Freudenthal Institute. The other is the work of Robbie Case at the University of Toronto.Pirie, Susan E. B.; Kieren, Thomas E.. Watching Sandy's Understanding Grow. Journal of Mathematical Behavior; v11 n3 p243-59 Sep 1992. 1992
Kieren, Thomas E.. One Point of View: Helping Children Understand Rational Numbers. Arithmetic Teacher; v31 n6 p3 Feb 1984. 1984
You can read about the work of the folks in Utrecht in:
Streefland, L.. The Design of a Mathematics Course. A Theoretical Reflection. Educational Studies in Mathematics; v25 n1-2 p109-35 1993. 1993You can read about the work of Robbie Case in:Streefland, Leen. Subtracting Fractions with Different Denominators. Studies in Mathematics; v13 n3 p233-55 Aug 1982. 1982
Streefland, L. (1991). Fractions in Realistic Mathematics Education. A Paradigm of Developmental Research. Dordrecht: Kluwer Academic Publishers.
Streefland, L. (1993). Fractions. A Realistic Approach. In T.R. Carpenter, E. Fennema & Th. A. Romberg (Eds.), Rational Numbers, An Integration of Research Hillsdale NY: Lawrence Erlbaum Publishers. (pp. 289-327).
Moss, Joan & Case, Robbie. (1999). Developing children's understanding of rational numbers: A new model and an experimental curriculum. Journal for Research in Mathematics Education, 30(2), pp. 122-147.