In recent years, a decreasing mathematical knowledge is observable among the first year university students. It is a problem also in Latvia. In the article different support measures taken by the Latvia University of Agriculture and the Riga Technical University to reduce differences in knowledge of mathematics is described: organization of mathematics refreshing courses, creation of e-materials, development of a new subject "Elementary Mathematics Sections”, additional consulting time, secondary school mathematics refreshing modules, etc. In order to assess the first-year students’ mathematics knowledge during the first math lesson the first-year students complete the diagnostic tests. To illustrate advantages of diagnostic tests in this article the results of the speciality "Civil Engineering and Constructions" diagnostic tests are analysed. The problem of this article is approached based on analysis and evaluation of scientific literature, a number of information sources and reports, taking into consideration the authors’ reflection, experience and observations.