Social cohesion in school is reflected in social discrimination processes and the complementary social roles of teachers, pupils, other staff and pupils' relatives. School social cohesion varies in level from high, characterised by prosocial interactions, to low, characterised by antisocial or violent interactions. Antisocial behaviour is usually embedded in specific interaction patterns between different social actors and is based on specific motives or stereotypes that elicit or justify this behaviour. Comprehensive study of these patterns is enabled by information and communication technology (ICT). The aim of this study is to use ICT to investigate social interaction patterns between personal and school characteristics of secondary school teachers and their curricular and disciplinary characteristics and experience of violence, including the motives they perceive when they are the victim, perpetrator or witness of six types of violence, differentiated according to the complementary roles of pupils, other teachers, other school staff and pupils' relatives. Three questionnaires were developed and used in a nationwide Internet-based survey in Dutch secondary schools. This school safety monitor was completed in 2006 by 5148 teachers, 80,770 pupils, 1749 educational support staff and 629 school managers. Data were checked for reliability, scale homogeneity and representativeness. Pearson correlation analysis was used to examine the social interaction patterns in teachers' data. The results reveal violence-specific social behaviour and social-mirroring processes between teachers and pupils in particular. Furthermore, teachers who are younger, female or working in low-attainment educational settings apply more curricular differentiation and collaborate more with pupils on disciplinary matters than their respective counterparts. Teachers who work in low-attainment schools, who work in cities, who are homosexual/lesbian or who do not feel most at home in The Netherlands experience more violent behaviour as a victim or witness than their respective counterparts. In particular, teachers attribute the following motives to violence: physical appearance, behaviour, level of school achievement, a handicap, being religious, gender, sexual preference and ways of dealing with non-conforming behaviour or punishments. Compared to teachers, pupils gave a broad array of motives for every type of violence. The conclusion is that Internet-based data-collection procedures provide a more comprehensive and systematic picture of social discrimination and violence motive patterns in schools than has hitherto been customary. (Contains 6 tables.)