Part of the reason for this is that we have not yet figured out reliable methods of accreditation, so that it is difficult for learners to convert their MOOC experience into qualifications that are relevant in the labour market. Holm Keller, former vice president of Leuphana University in Germany, developed an interesting collaborative variant of a MOOC for PISA, called PISA4U.20 He asked potential learners, most of them professional educators, to subscribe to a course and then grouped them based on an algorithm so that members of the group shared common aspirations about their education goals, but were as diverse as possible in virtually every other way. Those diverse groups then identified and worked on problems collaboratively, with each individual supported by an online mentor, and each group supported by an experienced tutor.