This study aimed to investigate the perceived collective teacher efficacy, teacher attitudes to inclusion of students with special educational needs, and the relationship between the constructs in a sample of Swedish teachers. The participants were 930 teachers involved in the Inclusive Behavioural Support in Schools implementation programme. The teachers answered the two questionnaires: The Teacher Attitudes to Inclusion Scale Swedish version (TAIS-Sw) and the Collective Teacher Efficacy Scale (CTES). The questionnaires were analysed and adapted to fit the sample adequately. This exploration identified a three-factor model for TAIS-Sw that is suitable for the data. The three latent variables related to classroom management, perception of the positive effects of inclusion for all students, and objections towards segregated special education. For CTES, a two-factor model showed a good fit for the data. The latent variables were related to aspects of teachers' competence, including belief in competency and skills to teach all students. The questionnaires identified positive expressions of collective teacher efficacy but more hesitant attitudes to inclusion. Structural equation modelling was used to investigate the relationship between the constructs of collective teacher efficacy and attitudes to inclusion, revealing a small positive relationship. Further investigations could help identify factors supporting successful inclusive practices.