In the field of Intelligent Tutoring Systems (ITS) the organization of the knowledge to be taught (curriculum) plays an important role. Different educational theories are used to organize the information, producing as many curriculum models as many ITSs exist. Most of these models are strict, leading to a teaching strategy unable to adapt itself to the student's learning strengths. In this paper first, we describe the design of a versatile curriculum model for teaching mathematics to low-attaining students, who need individualized teaching. Next, we report on the development of an adaptive to the student's strengths assessment system. In this report, we focus on the curriculum aspect and on the authoring environment, which has been developed to support curriculum editing. Finally, the evaluation of the assessment system, concerning the effectiveness of the curriculum modeling and the usability of its authoring environment, is presented.