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The research on deductive reasoning in mathematics education has been predominantly associated with the study of proof; consequently, there is a lack of studies on logical reasoning per se, especially with young children. Analytical reasoning problems are adequate tasks to engage the solver in deductive reasoning, as they require rule checking and option elimination, for which chains of inferences based on premises and rules are accomplished. Focusing on the solutions of children aged 10–12 to an analytical reasoning problem proposed in two separate settings—a web-based problem-solving competition and mathematics classes—this study aims to find out what forms of deductive reasoning they undertake and how they express that reasoning. This was done through a qualitative content analysis encompassing 384 solutions by children participating in a beyond-school competition and 102 solutions given by students in their mathematics classes. The results showed that four different types of deductive reasoning models were produced in the two venues. Moreover, several representational resources were found in the children’s solutions. Overall, it may be concluded that moderately complex analytical reasoning tasks can be taken into regular mathematics classes to support and nurture young children’s diverse deductive reasoning models.

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ResumoNeste artigo adotamos uma perspetiva de demonstração como forma particular de argumentação matemática. O estudo apresentado envolve uma experiência de ensino no 9.º ano, na qual foram tratadas propriedades do triângulo e seus pontos notáveis. Este estudo segue uma metodologia qualitativa, de carácter interpretativo. Os dados provêm de observação participante, gravações de áudio e vídeo das aulas, produções dos alunos com papel e lápis e no computador e de entrevistas. A partir de figuras construídas no Geogebra, os alunos estruturaram ideias matemáticas e raciocínios e construíram cadeias argumentativas. Os dados analisados mostram que a maioria dos alunos formula e explora conjeturas, procurando caminhos para a sua justificação. Os alunos reconhecem a importância do Geogebra na sua atividade como fator motivador e, acima de tudo, por permitir experimentar e manipular figuras. Os resultados apontam a importância da atividade com o Geogebra, na construção e manipulação como ponto de partida para a demonstração. Palavras-chave: Demonstração. Geometria. Geogebra. Triângulo. Reta de Euler. AbstractIn this study, we adopt a perspective of proof as a particular form of argumentation in mathematics. The study involves an experiment developed with 9th grade students, in which activities related to the triangle and its centres were proposed and carried out. This study follows a qualitative methodology of interpretative nature. Data were collected through participant observation, audio and video recordings of classes, student productions with paper and pencil, and with computers and interviews. Starting with the construction of figures in Geogebra,