The Dutch Ministry of Education, Culture and Science has funded a five years program to encourage the use, creation and sharing of Open Educational Resources (OER) by teachers from various types of education. This program is known as Wikiwijs. Ultimo 2013, the program has come to an end. As some of the assumptions at the start of Wikiwijs proved to work out in unexpected ways the lessons learned could fuel the next steps in developing Wikiwijs. Besides, other national initiatives on "opening up education" may also benefit from the lessons learned reported here. The main conclusion from five years Wikiwijs was that to accomplish mainstreaming OER, the Wikiwijs program should go along with other interventions that are more oriented toward prescriptive policies and regulations. In particular: the Dutch government should be more directive in persuading executive boards and teachers on schools to adopt OER as an important part of educational reform and the acquisition of 21st century skills. [This paper was presented at the OpenCourseWare Consortium Global Conference (Ljubljana, Slovenia, April 23-25, 2014).]