This article focuses on the design of a participatory diagnosis within a participatory action research (IAP) approach. The first part presents the theoretical aspects of this research method aimed at social change and transformation. It highlights the basic characteristics, key elements, the importance of the motor team, and the structural phases of IAP. The second part provides a practical example of a participatory diagnosis conducted in three secondary schools in L'Hospitalet de Llobregat, Spain, to contextualize the territory and identify the pathways and level of participation of young people. The theoretical aspects presented in the first part, combined with the practical example in the second, allow reflection on the integration of the three defining elements of this methodology: research, action, and participation. This approach involves a rethinking of the epistemological and methodological foundations based on critical analysis with active community participation to encourage transformative action and social change. The article discusses the characteristics of IAP, including its goal of transforming reality, the complexity of social reality, the mobilization and emancipation of social groups, systematic information collection, and the integration of reflection and action. It also outlines the key members of an IAP: the research team, the participatory action research group, and the follow-up committee. The IAP includes a spiral of research and action cycles, with central axes such as the definition of objectives, the development of a participatory diagnosis, the implementation of proposed actions, and the evaluation of these actions. A key phase in IAP is the participatory diagnosis of the context or community. This diagnosis is an opportunity to build integrated relationships and proposals to address the needs in the territory. The article presents the design of a participatory diagnosis conducted in a study in L'Hospitalet de Llobregat, focusing on the lack of participation among secondary students. The study aims to increase the community participation of secondary students (14-16 years old) in the city. The objectives include analyzing the participation of students, identifying participation channels, understanding the territorial context, promoting integrated actions to encourage participation, and evaluating the actions and the model used by the participatory action research group. The design of the diagnosis involves selecting and developing information collection techniques such as questionnaires, group discussions, observation, sociograms, documentary analysis, participatory days, and interviews. The research team, composed of educators and representatives of social entities, participates in the design of these techniques. The study uses a mixed method design, including quantitative, qualitative, and participatory techniques. The article also highlights the importance of reflection and the need to differentiate between actions that result from the diagnosis and those that do not. It emphasizes the need for proposals that include the challenges of this research methodology and distinguish it from other processes that do not require systematicization or scientific rigor.This article focuses on the design of a participatory diagnosis within a participatory action research (IAP) approach. The first part presents the theoretical aspects of this research method aimed at social change and transformation. It highlights the basic characteristics, key elements, the importance of the motor team, and the structural phases of IAP. The second part provides a practical example of a participatory diagnosis conducted in three secondary schools in L'Hospitalet de Llobregat, Spain, to contextualize the territory and identify the pathways and level of participation of young people. The theoretical aspects presented in the first part, combined with the practical example in the second, allow reflection on the integration of the three defining elements of this methodology: research, action, and participation. This approach involves a rethinking of the epistemological and methodological foundations based on critical analysis with active community participation to encourage transformative action and social change. The article discusses the characteristics of IAP, including its goal of transforming reality, the complexity of social reality, the mobilization and emancipation of social groups, systematic information collection, and the integration of reflection and action. It also outlines the key members of an IAP: the research team, the participatory action research group, and the follow-up committee. The IAP includes a spiral of research and action cycles, with central axes such as the definition of objectives, the development of a participatory diagnosis, the implementation of proposed actions, and the evaluation of these actions. A key phase in IAP is the participatory diagnosis of the context or community. This diagnosis is an opportunity to build integrated relationships and proposals to address the needs in the territory. The article presents the design of a participatory diagnosis conducted in a study in L'Hospitalet de Llobregat, focusing on the lack of participation among secondary students. The study aims to increase the community participation of secondary students (14-16 years old) in the city. The objectives include analyzing the participation of students, identifying participation channels, understanding the territorial context, promoting integrated actions to encourage participation, and evaluating the actions and the model used by the participatory action research group. The design of the diagnosis involves selecting and developing information collection techniques such as questionnaires, group discussions, observation, sociograms, documentary analysis, participatory days, and interviews. The research team, composed of educators and representatives of social entities, participates in the design of these techniques. The study uses a mixed method design, including quantitative, qualitative, and participatory techniques. The article also highlights the importance of reflection and the need to differentiate between actions that result from the diagnosis and those that do not. It emphasizes the need for proposals that include the challenges of this research methodology and distinguish it from other processes that do not require systematicization or scientific rigor.