The purpose of this study was to examine the factors that influence the attitudes of students towards peers identified as having special educational needs (SEN) in Portuguese mainstream schools. Data were collected from a sample of 1093 students from 5th to 9th grade across Madeira Autonomous Region. Data collection instruments included the "Chedoke-McMaster Attitudes Towards Children with Special Needs Scale" and a brief questionnaire covering sociodemographic and proximity information and knowledge about special needs. The results of multivariate analysis indicate more favourable attitudes in girls, younger participants and those with lower educational levels. Additionally, proximity, contact and knowledge related to special educational needs appear to be determinants of positive attitudes. The discussion of inclusion in schools and gender appear to be the factors most associated with students' attitudes towards peers with special educational needs in mainstream education. Implications and further studies are presented.