The inclusion of pupils into schools of the main educational stream is emphasized at the international level. Recently, this trend is more strongly applied in post-communist countries, where the now-criticized approaches (based on the exclusion of pupils with mild intellectual disability and behaviour disorders--e.g. ADHD--and their inclusion into special schools) persisted for a long time. Currently, the discussion on appropriate educational approaches which should be applied is now under development. Contemporary tendencies emphasize principles of so-called inquiry-based learning (IBL). This is the reason why the authors of this article compare published research conclusions at the international level. A number of them bring findings that the application of IBL influence positively the pupils with mild intellectual disability and behaviour disorders. However, there are also some researches that do not prove this finding. Based on the comparison, the authors conclude that the application of IBL positively contributes to the development of thinking of pupils with mild intellectual disability and behaviour disorders (ADHD).