Numerous studies show that a successful implementation of inclusion of children with special needs (SN) largely depends on the teachers' positive attitude towards it. The empirical research that is presented in the main part of the article analyses attitudes of a representative sample of Slovene teachers (n = 1360) regarding four domains of impact (impact of inclusion on pupils with SN, on peers, on teachers and on the classroom environment). In this, we controlled the role of the following two relevant characteristics of the sample: the category of SN (physical impairments, mild intellectual disabilities, learning difficulties and behavioural/emotional disorders) and the category of professional expertise of teachers in working with pupils with SN. We applied the "Impact of Inclusion Questionnaire". The results show that teachers' attitudes towards inclusion are determined by the type of SN the integrated pupils have. In the case of pupils with physical impairments, teachers expressed the highest level of consent and the lowest in the case of pupils with behavioural and emotional disorders. Our study shows that besides the type of SN, teachers' professional expertise in working with pupils with SN is another important factor that determines the level of agreement with inclusion. It turned out that the teachers who had taken part in different forms of education and training had a more positive attitude towards all domains of impact. (Contains 28 tables and 1 note.)