The use of complex and dynamic systems modelling to social systems is quite recent and its pertinence in the case of an educational system is continually increasing. For the concrete management of educational systems, a global approach is required. This approach must take into consideration the effects of many parameters that can act and interact together thus making, as a result, the system more or less efficient. Our aim is to develop a model that can capture the dominant dynamics of these systems while being at the same time simple enough to be useful for analyzing, simulating, and quantifying the impact of different parameters on the global performances of educational systems. By viewing education systems as skills production systems and by applying Business Processing modelling methods, a modelling of education systems is proposed in the present work which allows studying the effects of a set of parameters on the behavior of the system and its performance. The focus will be done on the study of the impact of learners' input competence on the performance of a training unit and on the performance of a training program. The obtained simulation results allow us to analyze the evolution of a training program's behavior as well as estimates its performance under the effect of the variation of simulation factors. These results enable to measure the performance variation according to the learners' input competence, their ability to acquire skills, and to the class size. This modelling enables us to test solutions for performance improvement.