It is provided through mainstreaming for children with special needs in order to get equal opportunities and get educated with their peers. In order to apply mainstreaming effectively, it is very important to provide suitable educational supports. However, considering our country's conditions, since there are not enough special education teachers in the field for service, educational support services cannot be provided enough. So, it is seen that other source/personnel are needed in order to give support to special needs students, their families, and teachers. Starting with these needs, development of an assistant teacher education program and evaluating its effectiveness is aimed in this study. The main purpose of this study is: a) to evaluate the effectiveness of education program for assistant teachers who will work in mainstream environments and b) to evaluate participant’s opinions for the education program. In this study, a single subject design; multiple probe design across subjects was used and replicated across subjects. Findings of the study was discussed according to the literature.