“…In this domain, research-based, content-specific explanations are crucial because "The teaching and learning of fractions is not only very hard, it is, in the broader scheme of things, a dismal failure" (Davis, Hunting, & Pearn, 1993, p. 63). Such view is consistent with numerous works about children's difficulties in learning fractions (Behr, Post, Harel, & Lesh, 1993;Behr, Harel, Post, & Lesh, 1992;Davydov & Tsvetkovich, 1991;Hiebert & Behr, 1991;Kieren, 1976;Mack, 1990;McLellan & Dewey, 1908;Smith, 2002). Besides pointing to possible difficulties involved in learning concepts related to the reversible fraction conception, this vast body of studies neither addressed the particular process in which this conception might be constructed, nor how the teacher might support its construction.…”