Changes in the social sphere, innovations in the field of information and communication technologies, the need for capable staff inevitably lead to a change in the current concept of the educational system. This change refers to the novelties introduced since preschool age, in the field of written expression, where the educational program would encourage the best possible development of children, whether they come from a typical population or have certain developmental disabilities. The aim of this research is to determine the effects of written expression in children of typical population and children with disabilities. The research sample consists of two hundred children of the typical population from the educational group and thirty children with developmental disabilities from the development group. During the testing of children from the typical population, a group of thirty children with disabilities emerged. In the further work, we called the obtained group of children an educational group of children with developmental disabilities. The revised version of the Peabody Individual Achievement Test (Revised) was used in the research to assess individual achievements, which enables the assessment of written expression. The individual testing process was conducted during September and October 2019. It was concluded that children of the typical population and children with developmental disabilities from developmental groups show better results on the subtest for written expression in contrast to the detected children with developmental disabilities in the educational group. The presented conclusion points to the need for greater engagement in adapting the preparatory preschool program with the inclusion of necessary exercises that stimulate the development of written expression in children with disabilities in educational groups, all with the aim of more successful inclusion.