In this paper we introduce a tutoring approach for ELearning formative process. This approach is strictly related to the assessment phase. Assessment in the context of education is the process of characterizing what a student knows. The reasons to perform evaluation are quite varied, ranging from a need to informally understand student learning progress in a course to a need to characterize student expertise in a subject. Finding an appropriate assessment tool is a central challenge in designing a tutoring approach. In this paper we propose a method based on the use of ontologies and their representation through a Bayesian Networks. The aim of our approach is the generation of adapted questionnaires in order to test the student?s knowledge of every domain?s subject. Analyzing the results of the evaluation an intelligent tutoring system can help students offering an effective support to learning process and adapting their learning paths.