We represent the main stages of the process of mathematical modelling as fuzzy sets in the set of the linguistic labels of negligible, low intermediate, high and complete success by students in each of these stages and we use the total possibilistic uncertainty as a measure of students' modelling capacities. A classroom experiment is also presented, illustrating the use of our results in practice. Our fuzzy model is compared to Markov models introduced for analogous situations in earlier articles. (Contains 1 table.)