In recent years, e-learning systems have become an important part of normal and university education. One reason for this is the growth in student numbers. INLOOP is an assessment system for object-oriented programming and is used in a beginner software engineering course of the TU Dresden. Unfortunately, for the course, there is no assessment system for object-oriented modeling. This thesis extends the INLOOP concept with functionality to assess object-oriented modeling. For that, it introduces INLOOM as a constraint-based model assessment system that works well with the architecture and workflow of INLOOP. It is based on a two-stage system that generates constraint-based test sets out of expert solution models and uses these to generate feedback and a score for a student's solution model. The system was designed by first surveying the literature on model assessment systems and then creating a design that is easy to include into INLOOP. To assess the new INLOOM system, a proof-of-concept realization for analysis UML class models is introduced. For evaluation, this realization is used to assess student solutions for tasks of multiple exams. The results of the assessment system are then compared with the assessments of human instructors. It could be shown that the INLOOM system works as well as other comparable systems. In conclusion, the INLOOM system can be used alongside INLOOP to improve the student feedback in the beginner software engineering course.