We present a probabilistic model, based on Dynamic Decision Networks, to assess user affect from possible causes of emotional arousal. The model relies on the OCC cognitive theory of emotions and is designed to assess student affect during the interaction with an educational game. A key element of applying the OCC theory to assess user affect is knowledge of user goals. Thus, in this paper we focus on describing how our model infers these goals from user personality traits and interaction behavior. In particular, we illustrate how we iteratively defined the structure and parameters for this part of the model by using both empirical data collected through Wizard of Oz experiments and relevant psychological findings. Categories and Subject Descriptors I.2.3 [Artificial Intelligence]: Deduction and Theorem Proving – uncertainty, “fuzzy”, and probabilistic Reasoning; K.3.1 [Computers and Education]: Computer Uses in Education – computer-managed instruction (CMI). General Terms Hum...