In the training as Biology teachers from the Francisco José de Caldas Distrital University, Faculty of Science and Education, our first approach to classroom in the Experimental Room takes place.In this context, the proposal to develop and implement the didactic unit called "Psychoactive Substances and Your Nervous System" was designed and implemented under the meaningful Learning pedagogical approach, during the months of April and May in 2011 at Manuela Sáenz school, located in the locality of San Cristobal in the south of the city.The practice was conducted with 901 grade students , aged between 13 and 17 years old, who had a misunderstanding about the concept of nervous system and the effect of psychoactive substances in it.Therefore, the unit had as main objective to make a conceptual and attitudinal change in students from their previous ideas, bringing them closer to a scientific understanding of the topics of psychoactive substances and the nervous system, enabling them a development in their ability to argue with scientific language and not only with their alternative knowledge.This paper accounts for the students learning processes, activities designed to achieve the necessary conceptual change approach based on meaningful learning and evidence of this process from the implementation of the didactic unit, as well as our contribution to undergraduate teachers training in the role of researchers, using the classroom as a laboratory and making the relevant reflections on the practice that could facilitate the teaching / learning.Este documento da cuenta del proceso de aprendizaje de los estudiantes, las actividades encaminadas para lograr el cambio conceptual necesario basadas en el enfoque aprendizaje significativo y las evidencias de dicho proceso a partir de la implementación de la Unidad Didáctica, además del aporte a nuestra formación docente en el rol de maestros investigadores, tomando como laboratorio el aula de clase y realizando las reflexiones pertinentes sobre la práctica que pudieron favorecer el proceso de enseñanza/ aprendizaje.