In The Netherlands, since a few years, universities experience a diminished level of basic mathematical skills of their new students. A lot of efforts have been put into understanding and solving of this problem, e.g., through the development of diagnostic tests and remediating materials. Also research activities have been performed. In this talk, some of the methods and results of this research are presented. These include methods to compare tests, e.g., the final exams at secondary school level and pretests of universities, and methods to measure and monitor the severity of the knowledge gap between secondary school and university.