Starting from educational aims that emphasise tolerance and understanding, the focus of this article is to analyse how difference is constructed in students informal relations, by enactments of bullying and sex-based and racist harassment. The article also discusses how young people themselves and teachers reflect on these kinds of processes. These questions are explored using data obtained from different perspectives: 1) ethnographic observations in secondary school classes of 7th graders; 2) interviews of the students in these classes (about 13 years of age); 3) interviews of the teachers that taught these classes; and 4) follow-up interviews of the same young people at the age around 18. The findings suggest that students individual diversities are sometimes constructed to "different-ness" in everyday life at school. "Different-ness" might be used as a reason for bullying, racism, or sex-based harassment. In schools this is not effectively addressed by teachers.