The convergence towards the European Higher Education Area (EHEA) entails the implementation of active teaching methodologies with the final goal of allowing students to develop new competences and skills. As a consequence, the degree of achievement of these competences has to be evaluated appropriately by means of the definition of formal and reliable evaluation processes. In this context, evaluating transversal/soft competences makes this goal specially challenging. This work introduces a method Based on Teachers Reasoning (BoTR) to allow the design of automatic assessment systems for the evaluation of transversal competences of students. BoTR defines a methodology that takes into account the subjective criteria applied by teachers when assessing the considered competence to build an automatic assessment system. After introducing BoTR, we apply this method to assess the teamwork competence for real students of engineering, describing the application of the three stages of the BoTR method in a real scenario.