An international online mentoring programme Open Education for a Better World (OE4BW) has been developed to unlock the potential of open education in achieving the UN Sustainable Development Goals. The programme provides an innovative approach to building Open Educational Resources, connecting developers of educational materials with experts volunteering as mentors. The model of the programme has been carefully designed and tested in two subsequent implementations in years 2018 and 2019. Results have proved the model to be useful for building capacities in open education, while producing concrete educational materials with great potential for social impact. Analysis of results has been used to suggest further improvements needed for enabling the program to be used on an even larger scale. The paper presents the development of the OE4BW model, its main characteristics, implementation results and guidelines for the future.