eng Science and Education Publishing American Journal of Educational Research 2327-6150 2017-12-06 5 11 1167 1171 10.12691/education-5-11-9 EDUCATION20175119 article Michael. Gr. Voskoglou 1 Department of Mathematical Sciences, Graduate Technological Educational Institute of Western Greece, Patras, Greece Grey numbers, which are defined with the help of the real intervals, are very useful in the everyday life for handling approximate data. In the present paper grey numbers are used as a tool for assessing, with linguistic expressions, the student understanding of the graphical representation of the derivative. Although the proposed new assessment method is proved to be equivalent with an analogous method using Triangular Fuzzy Numbers developed in earlier works, the required computational burden is significantly reduced. A classroom application is also presented illustrating our results. http://pubs.sciepub.com/education/5/11/9/education-5-11-9.pdf teaching the derivatives assessment methods grey Numbers (GNs) whitenization