In this paper, we propose a scheme for evaluating learners? knowledge level on concept mapping tasks. The assessment process focuses on the propositions presented on learner?s map as well as on the missing ones with respect to the propositions presented on expert map. The evaluation of learner?s knowledge level depends on the weights assigned to the concepts and propositions on expert map as well as to specific categories of errors that may be identified on learner map. The proposed scheme has been embedded in COMPASS, an adaptive web-based concept map assessment tool. An application example of the evaluation of learner?s knowledge level and the performance feedback provided are presented.