En la presente tesis doctoral se ha estudiado la agresión y sus consecuencias con 519 alumnos desde 1º de la ESO a 1º de Bachillerato. Hemos examinado diferencias entre grupos según sexo, edad, nacionalidad y características de la personalidad. Hemos explorado como la personalidad y el afrontamiento que emplean las víctimas pueden afectar a la severidad de la agresión al que están sometidos, así como la naturaleza y gravedad de los síntomas psicológicos que padecen. Además, se ha utilizado una novedosa técnica de mediación múltiple para identificar y cuantificar el papel que juega la personalidad y la forma de afrontar los estresores en el desarrollo de problemas psicológicos a raíz del acoso escolar. Al examinar la frecuencia y naturaleza de agresión en los centros escolares, encontramos que los niños experimentan más agresión física y castigo mientras las niñas sufren más agresión indirecta. Ambos grupos manifiestan niveles casi idénticos en agresión verbal. Las niñas padecen más síntomas en general que los niños a raíz de sus problemas en la escuela. Los españoles fueron agredidos físicamente con más frecuencia y fueron castigados más que los inmigrantes. Los estudiantes más jóvenes sufrieron niveles ligeramente superiores que sus compañeros mayores, salvo en agresión indirecta. Por lo general las agresiones verbal e indirecta guardan una mayor relación con síntomas psicológicos adversos. Se han estudiado cinco características de personalidad, dos de ellos de componente emocional (neuroticismo y extraversión) y tres de tipo cognitivo (estilos de afrontamiento – interiorización, exteriorización y referencia a otros). La interiorización (autoinculparse, ignorar u ocultar el problema) es lo que más perjudica el bienestar psicológico de la víctima. El neuroticismo es otra variable de gran influencia en la aparición de todo tipo de síntomas como resultado del acoso. La referencia a otros (apoyo espiritual y profesional, acción social) también es contraproducente, pero en menor grado. Las víctimas más introvertidas manifiestan niveles más altos de conducta oposicional, evitación, hiperactivación y sintomatología general. La única variable que demuestra tener un efecto mediador positivo es la exteriorización (apoyo social, diversiones, hacer esfuerzo). Estás victimas manifiestan niveles más bajos de síntomas, particularmente desesperanza, regresión, miedos i evitación.In this doctoral thesis, aggression and its consequences have been studied with 519 middle and high school students in the city of Valencia, Spain. The differences between groups based on gender, age, immigrant status and personality characteristics have been explored. The influence that personality and coping style have on the severity of the aggression that victims face, as well as the nature and severity of the psychological symptoms that they suffer, has been examined. Additionally, multiple mediation has been used in order to identify and quantify the role that personality and coping have on the development of psychological problems resulting from school bullying. When studying the frequency and nature of aggression in schools, we find that boys experience more physical aggression and punishment while girls suffer more indirect aggression. Both groups manifest very similar levels of verbal aggression. Girls report more symptoms than boys as a result of their problems in school. Spanish natives were physically victimized and punished more frequently than immigrants. Levels of verbal and indirect aggression were very similar among these two groups, with the exception of teasing related to their ethnicity or race, much more common in immigrants. Younger students manifested slightly higher levels of victimization, except for indirect aggression. When considering each event individually we find that older children usually suffer more thought-out and severe aggression, while younger students use more simple and less personal aggression. In general, students that experience verbal and indirect aggression have a higher incidence of adverse psychological symptoms. When we examine the differences between bullied and non-bullied children, it becomes clear that the former manifest many more psychological symptoms in general, particularly post-traumatic stress, depression and hypervigilance. Girls generally report more symptoms than boys as a result of adverse school events. This tendency is maintained, although to a lesser degree, when we study those that have been bullied. These same analyses carried out with groups formed using the other demographic variables show very few differences. The personality characteristics of neuroticism and introversion as well as three coping styles (interiorizing, exteriorizing and reference to others) were studied in relation to victimization and symptoms. Using regression and multiple mediation analyses we found that the use interiorizing coping (self-blame, tension release and ignoring or hiding problems) is the most detrimental to the well being of the student. Of this coping style, the most ineffective mechanisms are blaming oneself and the screaming and crying that characterize tension reduction. Neuroticism is another variable that greatly influences the emergence of psychological symptoms as a result of bullying. The tendency to center on negative experiences and emotional instability can exacerbate psychological symptoms and make the person a more viable target for future aggression. The coping style of reference to others (seeking spiritual and professional help, social action) is also counterproductive, but to a lesser degree. Students that use this style frequently usually have more psychosomatic difficulties and generalized fears. Of the three mechanisms, seeking spiritual help is the most counterproductive, probably due to its passivity. More introverted victims manifest higher levels of oppositional conduct, avoidance, increased arousal and general symptomatology. However, the mediating role of this personality characteristic is less significant than those mentioned above. The only variable shown to have a positive mediating effect is exteriorizing coping (social support, relaxing diversions, making an effort). These victims manifest lower levels of symptoms, particularly hopelessness, regression, fears and avoidance. Making an effort and being successful, social support, and belonging are the most effective ways of dealing with problems of peer aggression.