The aim of this paper is to present the results of a two-year speech production training of hearing impaired children with the help of a Speech Assistant system developed as part of a research that has been carried out as a cooperation between the University of Debrecen and the University of Miskolc in the framework of the project called ’Basic and Applied Research for Internet-based Speech Development of Deaf and Hard of Hearing People and for Objective Measurement of Their Progress’. The project is aimed at solving basic and applied research tasks to develop an application for supporting the improvement of speech production of deaf and hard of hearing people more effectively than the methods known already. The idea of the Speech Assistant has come from an audio-visual transcoder for sound visualization developed at the University of Debrecen, and a three-dimensional head model for articulation presentation, called ‘talking head’ developed at the University of Miskolc. The most important aim of the research is to create a complex system to assist the speech production improvement of hearing impaired children by the visualization of speech sound and articulation. However, it is important to note that personal contribution of specialized teachers cannot be replaced. The module performing the audio-visual transcoding required is language-independent, the talking head and the automatic assessment of utterance can be adapted to other languages. While in 2015 an earlier state of the research has been introduced in the International Scientific Conference on Advances in Mechanical Engineering, this paper is presenting new results and conclusions as well.