In recent decades, the parental involvement in their children's education has been recognised as a value that has had numerous positive effects on the children, their parents, the school, as well as the entire community in which the children are raised and educated. The development of parent partnership requires a major shift in the traditional school and parent relationship, as well as the establishing of new relationships based on voluntariness, trust, respect, competence, communication and equality. The students with developmental disabilities need a parental partnership between the parents and the school as it provides them with the optimal development, whereas the traditional approach which is still prevailing in school practice makes it extremely difficult for them to fully integrate into the society and reach their full potential. However, the 21st-century school has not fully achieved the totality of inclusive education requirements yet, and the students with developmental disabilities and their parents still lack the appropriate approach, initiatives and acceptance. Individual investments of the parents of the children with developmental disabilities in home schooling are particularly important, because they contribute to their children's overall development, as well as their academic and social development. Likewise, the parents of the students with developmental disabilities have a need to participate more frequently and purposefully in school activities, as well as communicate with teachers and other school professionals. There is still a lack of a comprehensive parent involvement program at the State or county level. This case raises questions aimed at encouraging a higher participation of parents in the education of children with and without developmental disabilities, as well as the questions concerning the role of the parents' satisfaction in having the opportunity to participate, i.e., to establish partnerships. The models that support the involvement of parents in their children's education are based on different starting theories, which themselves have evolved under the influence of social changes, as well as democratisation and liberalisation processes. There is a long development path from parental involvement in their children's activities to the parents' acceptance that is still in its early stage. The paper takes the Bronfenbrenner's bioecological theory (2004) and Epstein's revised theory of overlapping spheres (2011) as starting theories. This PhD thesis consists of both the theoretical and the empirical part. The theoretical part provides the analysis of the historical development of the relationship between the parents and the school, as well as the peculiarities of the development of the relationship between the school and the parents of children with developmental disabilities, including the theoretical starting points and parental involvement models, the forms and limitations of their involvement, the school and home characteristics in the light of the parents' investment into their education, with particular focus on the investment of the parents of the children with developmental disabilities in their education. The paper also examines the characteristics of the parents and children with developmental disabilities in the context of education and their life circumstances. Their satisfaction with the school is considered a potential predictor of the parental involvement in the education of students with and the ones without developmental disabilities. The empirical research is based on a survey conducted on parents divided into two subgroups, with the purpose of identifying a link between the parents' involvement in their children's education and their satisfaction with the school. The survey was conducted on thirteen different schools in northwest Croatia with the parents of the second and sixth grade students who are educated in regular elementary schools, of whom 6.36 % had developmental disabilities. The developmental disability criteria were the appropriate form of education prescribed, the regular education program with personalised procedures and the regular education program with the adapted materials and personalised procedures. A total of 896 surveys was completed. The research conducted shows that parents are most satisfied with the school and that there is no difference between the subgroups of parents. Moreover, little difference has been found in the parental involvement in the education of students with developmental disabilities and the ones with no developmental disabilities, as well as in the family and school activities and communication. Although at first glance such results indicate the equal attitude the school shows towards everyone, they actually suggest the parents of the children with developmental disabilities have not been recognised to the appropriate extent in terms of their efforts and investments, nor has the need for their greater involvement. Such an interpretation is also supported by the fact that the parents of the children with developmental disabilities are more involved in the activities at home, which could be interpreted as providing their children with a greater self-indulgence and leaving them to their own devices. The theoretical analysis and the empirical research raise a number of issues and call for a satisfactory response to the specific needs of the children with developmental disabilities and their parents during their schooling in order to meet the inclusive education and society requirements. The society development level is seen in its care of the most vulnerable and this PhD thesis can certainly be an important lever in raising the quality level of the Croatian society in this respect.