Former literature found that various 'different' students experience exclusion and rejection by their peers in schools. This may be linked with the attitudes that their school and classmates hold towards them. Identifying someone as 'Other' may indeed result in prejudicial attitudes which, in turn, can lead to his/her marginalisation and exclusion. From an inclusive perspective, it is thus pivotal to explore student attitudes towards the conceived different ones and how they are linked with exclusionary patterns among peers in schools. To contribute to the understanding of the link between peer attitudes, diversity and exclusion, the present paper reports on the stages of development of an instrument aimed to measure adolescents' attitudes towards otherness which combines a qualitative and a quantitative approach. Beside measuring their attitudes, the instrument also investigates students' representations and definitions of otherness. Such representations -- as emerged from the pilot study of the instrument -- will be presented here. The findings confirmed the importance of adopting a wider and non-categorical approach to otherness in the study of peer attitudes and exclusionary processes in schools.