The study allows us to identify the effect of observer training on pro-social and assertive behaviors in school bullying in a school in the city of Bogotá located in the town of Bosa. 64 students were taken between 12-14 years of 6th, 7th and 8th grade of high school, selected by sampling by conglomerates. The design was quasi- experimental pre-test post-test with control group. The Questionnaire on Intimidation and Maltreatment between Equals was applied- INSEBULL (Avilés & Elices, 2007) selecting the population and homogenizing the groups, participants were linked by random assignment in groups. The Scale of pro-social skills for adolescents EHPA (Morales & Suárez, 2011) and the Assertive Behavior Scale for Children (CABS) (Wood,1978) was applied, from the above the GE training was developed, evaluating it through the post-test of the INSEBULL, EPHA and CABS. The results allow to reject the hypothesis of work established for the study, and the null hypothesis is accepted, which specifies that the training in observers in pro-social and assertive behaviors does not establish significant differences in their measurements, for which no changes are observed. in the dynamics of the phenomenon of School Bullying.El estudio permite identificar el efecto del entrenamiento a observadores en conductas pro-sociales y asertivas en el bullying. Se tomaron 64 estudiantes entre 12-14 años de 6°, 7° y 8°,  seleccionados  mediante muestreo por conglomerados.  El diseño fue cuasi-experimental pre-test pos-test con grupo control. Se aplicó el Cuestionario sobre Intimidación y Maltrato entre Iguales- INSEBULL, seleccionando la población y homogenizando los grupos,  se vincularon participantes mediante asignación aleatoria en grupos.  Se aplicó la Escala de habilidades pro-sociales para adolescentes EHPA y la Escala de comportamiento asertivo para niños (CABS). Se desarrolló el entrenamiento al GE,  se aplicó el pos-test del INSEBULL, EPHA, y CABS, encontrando resultados opuestos a las hipótesis de trabajo.