Despite the opportunities and benefits of OER, research and practice has shown how the OER repositories have a hard time in reaching an active user-base. The opportunities of experience exchange and simple feedback mechanisms of social software have been realized for improving the situation and many are basing or transforming their OER offerings towards socially powered environments. Research on social software has shown how knowledge-sharing barriers in online environments are highly culture and context-specific and require proper investigation. It is crucial to study what challenges might arise in such environments and how to overcome them, ensuring a successful uptake. A large-scale (N = 855) cross-European investigation was initiated in the school context to determine which barriers teachers and learners perceive as critical. The study highlights barriers on cultural distance, showing how those are predicted by nationality and age of the respondents. The paper concludes with recommendations for overcoming those barriers.