It proves that many starting students at Technical Universities don’t have the required mathematical knowledge and abilities. This is caused by educational gaps at secondary schools, disinterest of students and a process of forgetting over time. At TUDelft a MOOC has been developed to train new students in mathematical calculus during the summer holidays before start of the academic year. The underlying didactic model is based on inquiry learning. The MOOCs can be downloaded on mobile devices and the used didactic model can be combined with cooperation and network learning.