This research report, which is presented below, arose from the need to strengthen the learning capacity of the seventh grade students of the Pradilla Departmental Educational Institution, El Colegio Municipality, department of Cundinamarca, through the development of argumentative skills that enhance the Development of critical thinking. Its main objective was to interpret and explain the argumentative strategies used by students when they face problems of environmental contamination; Through the design and application of a didactic proposal. The methodology used was a qualitative study, where the written and oral answers of the students who intervened in the research were carried out (20 students) to whom the instruments were applied (pre-test, didactic intervention and post-test) With the aim of identifying the argumentative strategies based on the categories presented by Toulmin, who at the same time triangulated with the categories on the nature of knowledge; For this, debates, forums and activities were developed that allowed to analyze argumentative episodes on the part of the students. The results derived from the analysis of the information allowed to show that the categories that students develop the most when they use argumentative episodes are assertions, data and guarantees, and the ones that use least are refutations and qualifiers. With respect to the nature of knowledge, their knowledge is initially based on beliefs or common sense, but at the same time that the implementation of the didactic unit was advanced, its knowledge was based on experience and scientific knowledge.