“…These include the theory of the development of geometric thinking by Dutch teachers Pierre van Hiele and Dina van Hiele-Geldof (Fuys et al, 1984;van Hiele, 1986). Noting the difficulties their students had in geometry, they developed a theory that introduces different levels of thinking that students go through as they move from simply recognizing a figure to being able to describe a formal proof (Clements & Battista, 1992;Crowley, 1987;Mason, 2009, Mason & Moore, 1997Sbaragli & Mammarella, 2010;Usiskin, 1982). Five levels are indicated by van Hiele (1986), which are sequential and hierarchical: level 1 (visualization), in which one recognizes figures only by their appearance without perceiving their properties; level 2 (analysis), in which one recognizes the properties of figures without, however, perceiving the relationship between them; level 3 (abstraction), in which one perceives the relationships between properties and figures without, however, yet understanding the role and significance of formal deduction; level 4 (deduction), in which one is able to construct demonstrations, understand the role of definitions and axioms and know the meaning of necessary and sufficient conditions; and, finally, level 5 (rigor), in which one understands the formal aspects of a demonstration.…”