Post Offices Inc. in The Netherlands has developed and implemented a new instruction model for the training of desk employees. The quality of the new instruction model was assessed by means of the evaluation model of Jacobs and Jones for on-the-job training. It is concluded that the implementation of the training model has not been completely successful. Critical success factors, such as the performance of the mentors as well as the quality of the self-study material, have to be improved. Mentors are expected to serve as a behavioural model, to provide feedback, arrange an adequate environment for self-study, motivate trainees for self-study and evaluate trainees’ progress on a regular basis. This study shows that mentors must be fully convinced of the benefit of a new instructional model, if not, the implementation will not be successful. Besides, the study shows that the quality of the self-study material depends very much on the similarity between the knowledge needed in work and the knowledge presented in the self-study material.