Uncertainty is a key feature of philosophising with children. It is central to the theory and methodology of philosophical inquiry and the educational assumptions underlying it. Uncertainty also presents a specific challenge for pupils and teachers undertaking philosophical inquiry in the classroom, because mainstream education is mostly based on certainty: reduction of complexity in view of assessment, a focus on students giving the right answers, standardized skills and competencies. This paper presents empirical research, reporting the reflections of primary school children and teachers on their experiences with philosophical inquiry in the classroom. It revisits the opportunities and challenges presented by philosophising with children in mainstream education and discusses the implications for teacher education.