The aim of the paper is to analyse the assessment of practical training as factor of quality assurance in the system of vocational education and training (VET). In Estonia, like in many countries with school-based VET system, one of the problems related to practical training in enterprises can be poor cooperation between schools and enterprises. The responsibilities of the different parties in the process of practical training are sometimes not clear at all. In this paper, Niklas Luhmann's system theory was taken as a theoretical framework in conceptualising existing assessment practices in the fields of training of nurses and IT specialists as acts of communication between schools, training workplaces and apprentices. The empirical data have gathered by semi-structured interviews with different stakeholders in the assessment process, including vocational schools, enterprises and students. In the context the Luhmann's system theory offered a useful framework for structuring empirical data. By conceptualising the assessment of practical training as acts of communication between systems some problems came to light.