The role of the family in the development of the child as well as the quality of the parent-child relationship and its effect in the social, mental and cognitive development of the child has been the focus of attention of many sciences and scientists and it has been discovered that many parents are not well prepared to do their best for their children. The parent training programmes are willing to partly give a solution to this with their preventive role. In recent years, the effectiveness of the parent training programmes, which are offered to "high risk" parents, has been the focus of a big amount of research, meta-analyses and reviews. A smaller amount concerns the effectiveness of the universal programmes which are offered to the parents of the general population. The effectiveness of a ten-meeting structured group parent training programme of cognitive-behavioral approach, which had been offered to mothers of the general population, was researched in the present study. It aimed to research the effectiveness of the specific programme in the children's behavior and the subjective perception of the functionality of the family of the mothers who chose to participate in and completed the programme (n=56, experimental group/participants), compared to those who chose not to (n=113, control group/non participants). The mothers of the two groups were mothers with children aged between 2 and 12 and filled in the Family Adaptation and Cohesion Scales, FACES-III and the Questionnaire of Inter-personal and Cross-personal Adaptation, before (Phases A) and after (Phases B) the programme. The two groups were fully matched and did not present any significant difference regarding their demographic characteristics. During both Phases A and B of the training programme participants and non-participants expressed a high degree of satisfaction by the functionality of their family and did not differentiate significantly in the evaluation of the existent family cohesion and adaptability, the type of the family based on the cohesion and adaptability and the general type of family based on the functionality. In addition, while the children of the participants were, before the start of the programme, in a significantly disadvantaged position compared to the children of the non-participants, after the end of the programme, they were significantly improved, decreasing the negative symptoms and behaviors. This particular parent training programme of cognitive-behavioral approach, as well as other programmes which belong to the same theoretical direction, could contribute to the prevention of the behavior problems and the promotion of the mental health.