The Field Education (FE) began to be conceived in the 1980s by Rural Landless workers. Little by little, as other social subjects were also caring about the issue, the FE was guided on the political agenda of the country and gradually, over the years of 1990s, it was consolidated as Policy of Field Education (PFE). The establishment of the PFE imposed and still imposes challenges to the professionals of field school to appropriate themselves of a new conception that guides their practices. The research objectives were to investigate how the teachers, coordinator and director of a field school in the countryside of São Paulo State appropriated the Policies of Field Education and understand what are the mediators that limit and enhance the process of appropriation. The theoretical framework was the historical-cultural psychology; our interest focused mainly on the concepts of mediation and appropriation of Vigotsky. The research was conducted in a school located in a land reform settlement area in the countryside of São Paulo, and had as subjects 5 teachers, a coordinator and a director. Data collection took place through questionnaire, semi-structured interviews and observation. Two interviews with each teacher and observations for a period of 14 days at the institution were conducted. In data processing, we attempted: to understand the meanings and significance about FE; map the mediators of the PFE appropriation process; understand how the mediators acted in the process of professionals' appropriation of the field school; grasp the mode of professionals' appropriation of the PFE field. Results show that: (1) the process of appropriation of PFE happened at different instances of the relationship of professionals with the FE and the rural space, for example, in the training course and in the engagement with the social movement; (2) the process of appropriation was influenced by different mediators of various types, such as the training and working conditions; (3) mediators were characterized by two ways of acting in the appropriation process of the PFE: as potential-changing mediators and limiting mediators; 4) the direction and speed of the appropriation process were determined by the movement produced by the relationship between mediators; (5) there was an articulation movement between mediators, this movement has shown that the appropriation happened from a game of forces between the mediators of the relationship of the teachers, coordinator and director with the policy of the FE; (6) there was an interrelationship between each professional appropriation processes; (7) the appropriation level of each professional was very similar because the changing-mediators of personal reasons lost strength when they passed to mediate the process of the group; (8) the group of professionals of the field school had a very fragile appropriation of the PFE. Finally, we conclude that the process of appropriation is defined by the relationships that professionals had with the PFE. Relations with politics were regulated b...