In this paper the fuzzy knowledge representation of a neural network-based fuzzy model is presented. The model is used to assess student's motivational state in a discovery learning environment. Student?s observable behavior and motivational factors are described with linguistic variables. The inputs of the model are tailored from real students? data, with the assistance of a group of expert teachers. Results of our preliminary study were encouraging, since data obtained from real students? log files, have been successfully used to form the membership functions that assign membership degrees to the linguistic values of the linguistic variables.