Background and aim: Teachers’ positive attitudes towards inclusive education are taken to be critical to providing education that better meets pupils’ learning. Studies have therefore tried to clarify interaction between teachers’ attitudes and inclusive education. The present study reports data on teachers’ attitudes, self-efficacy and collaboration towards inclusive education in Sweden. Nation-wide data were collected from teachers before they joined a national professional development programme aimed at strengthening schools' competence in adapting teaching to the conditions and needs of pupils. Methods: Participants were 2,348 (51,6%) out of 4,553 targeted teachers that answered an online survey. The survey included three instruments: the Ohio State Teacher Efficacy Scale (OSTES), the Sentiments, Attitudes and Concerns about Inclusive Education – Revised (SACIE-R), and bespoke questions about teachers’ attitudes towards collegial learning (TACL). Mean values and correlations were assessed. Responses to an open question about teachers’ expectations ahead of starting their training programme were analyzed in NVivo, using word frequency analysis. Results: Three-quarters of respondents show overall positive responses towards adapting their teaching to the conditions and needs of pupils. However, almost two-thirds of teachers do also report significant concerns about their ability to do inclusive education well. Scores remained largely unaffected by public or private school ownership, nor did the affluence of school catchment areas affect teacher scores. Conclusions: The self-reported attitudes, self-efficacy and collaboration among teachers in Sweden towards adapting their teaching to the conditions and needs of pupils support positive research conclusions: although they do have concerns likely to be founded on professional considerations, teachers are by and large positive about meeting pupils’ learning needs.