The presence of children living on the streets of the big cities, it is one of the situations which produces the most concern, amazement and compassion on people; however, these people and even institutions in the social field, disregard the factors that generate this problem.

These facts have motivated the Bogotá YMCA to first onvolved in get the preventive field, with the conviction that this approach and its methodology are not only effective but also its social profitability is highly superior to the traditional models focused on re-education.

Although in 1986,the Bogotá YMCA restructured the focus on the work with street children and directed its efforts towards Home Abandonment Prevention Program and all the phenomena associated with this problem. Recently, we have gladly seen the Colombian Government adopt prevention as an important part of its development plans.

We introduce a set of tools and methodologies which constitute the preventive model "Development Pyramid". The evolutional process of the proposal was built on research that let the YMCA find the key aspects that cause home abandonment and develop a methodological proposal which incorporates thefollowing components:

• Approach and motivate action with street children in their own environment.
• Work with " expeller" families.
• Community organization processes in high risk sectors.
• Support process of inter-agency coordination in different fields.
• Stimulation of productive and profitable activities.

After thirty years working with or in the area of street children, their families and their communities, we have accumulated significant experience with emphasis on prevention, we feel the need to share the results of this work, because we are sure it is possible to reapply this knowledge in similar problematic contexts.

This workis dividen into five chapters in which the themes/strategies/methodology´s are developed.

1.Context Analysis: A reading of the reality is presented briefly, which lets us understand the reasons associated with the children problematic (boys, girls and/or youth) on the street environment and the main aspects that must be taken into account for the positive transformation for their life project.

2.Phylosophical Framework: The institutional reasons and principles which inspire and make good sense of the project.

3.Conceptual Framework: Some primary concepts let have allowed us to theoretically support the Home Abandonment Prevention Program. They have been the framework to do the methodological propositions.

We have selected the main focuses to direct the conceptual discussion about our preventive perspective. The topics to discuss in this chapter are:

3.1 Rights perspective
3.2 Systemic-socio-ecological concept of the human development
3.3 The Social Stress Model applied to the violence within the family and children mistreatment(Mossavi)
3.4 Social Networks

4.Methodology: Taking into account the institutional framework, we have developed the YMCA's Methodological Proposal. It is based on the concept of Integral Development which articulates operative and technical processes based on its philosophy, objectives, principles and values.

5.Home Abandonment Prevention Program: Every technique and strategy which has been adopted in the preventive model of the YMCA of Bogotá are developed in this chapter. As a starting point to the description of each phase of the program, the history and evaluation of the Home Abandonment Prevention Program are presented. We consider it relevant to include the history of the program, to help understand and comprehend the factors that motivated us to make the proposal. The text includes the reflexions and institutional experiences.

Every phase of the program is described below; they include:

1. Approaching and contacting street children
2. Preventive Reception Centre for children (on their first stage of living on the street)
3. Work with underprivileged families with antecedents or in risk of their children abandoning their homes
4. Community organization and promotion

Besides some components which touch and affect this project directly are taken into account, those components are:

• Actions too prevent school drop out
• Encouragement for Productive and Profitable Activities
• Inter-agency Coordination
• Social Policies

Finally we will take into account the technical aspects that need to be considered to develop the program successfully.

Through this work we want to generate reflexions about the proposal and focus on people living on the streets, emphasizing how important it is to develop a global and integral vision about such a complex problem.