In the field of Psychology and Didactics of Language many researches on the acquisition and learning process of argumentative discourse among elementary school students have led us to approach this discursive competence based on the parameters of adult mode of writing arguments. As a result, studies on the subject matter tend to conceive the children`s essays in terms of inadequacy and lack of proficiency; and as consequence of its complex cognitive demands the teaching of argument has been belated to the end of elementary school curriculum (14-15years old). The implicit hypothesis behind this procedure is that there is a graduation-succession for the learning of discursive genres in a way that narrative and descriptive genres should precede systematic teaching of argumentation. The prime goal of the present research is to determine to what extent 8-11 year-old pupils have represented for themselves the argumentative schema when they are asked to write an opinion essay as a school task. The second one is to identify how this textual schema is carried out by the learning children and textualized into written mode of language, considering (1) children`s cognitive development level to deal with the dialogic dimensions of written discourse; (2) the turn-take conversation influences on their writing, and (3) children`s lack of formal learning of argumentative genres in school curriculum. For this purpose we took as our basis on the sociocognitive hypothesis of language acquisition and on socionteracionist approach of language. The research analyses a longitudinal corpus composed of 145 essays produced by the same elementary school students from 2nd grade up to the beginning of 5th in a public school. The students were asked to write five different opinion essays. The analysis is split into two main focuses: the first one highlights the way the learning children build their written opinion in terms of textual configuration through both articulation and coordination of textual sequences; the second focus highlights the nature of arguments chosen by the learning children in terms of epistemological attitude and evidenciality. The research confirms that in the genre of argument and expressions of opinion, most of the children displays a particular knowledge to categorize communicative events of language in use, although the cognitive model triggered to convince and persuade the addressee could not necessarily suit the adult prototype schema and school expectations. At the same time, it also shows that a simple argumentative disposal does not determine beforehand the textual schema triggered by the children to frame their argumentation; contextual and sociocognitve features also determine the pragmatic, discursive and argumentative dimension of the text. Due to the features shown in the present research, and as far as pedagogy and didactic of language is concerned we defend that systematical and progressive teaching of argumentation should begin as early as possible in school context.