 The Development of Proportional Reasoning: Grade 6 Students’ Trajectories Ana Isabel Silvestre Escola EB 2,3 Gaspar Correia, Portela Doctoral student at the University of Lisbon anaisabel.silvestre@sapo.pt Introduction Research indicates that students’ ability to reason proportionally is important for their own mathematical development. This kind of reasoning is fundamental to solve some daily life problems and is also essential for learning advanced mathematical topics as well as physics and chemistry (Abrantes, Serrazina & Oliveira, 1999; Post, Behr & Lesh, 1988). However, research indicates that students’ ability to reason proportionality is limited (Bowers, Nickerson & Kenehan, 2002; Van Dooren, De Bock, Hessels, Janssens & Verschaffel, 2005). Some authors claim that this limited ability is related to curriculum shortcomings (Behr, Harel, Post & Lesh, 1992; English & Halford, 1995; Spinillo, 1993; Streefland, 1985), as the subject direct proportion is often taught stressing the use of the “rule of three” in missing value problems (Robinson, 1981). In the case of Portugal, the official documents suggest just a small number of lessons to this topic, not adjusted to the importance of proportional reasoning, not the time necessary for pupils to appropriate with real understanding. However, there is strong evidence that students who are encouraged to construct their own knowledge on proportion through collaborative problem solving activities, perform better than students with more traditional, teacher-directed instruction (Ben- Chaim,, Fey, Fitzgerald, Benedetto & Miller, 1998; Silvestre, 2006). This study concerns the way grade 6 students learn about direct proportion, when they are involved in a teaching experiment based on investigative and exploratory activities and problems and also on the use of a spreadsheet. The central aim of this study is to understand the students’ strategies and data representations in common proportion problems as they are encouraged to construct their own conceptual and procedural knowledge. To reach this objective I will look to answer to the following questions:  What are the strategies used by students for solving direct proportion problems? What it takes them to opt for one or another strategy? How are these strategies related with their knowledge of the conceptual field of the multiplication?