This study presents the results of the Preschool Inclusion Project investigating the effects of inclusive preschools on the development of children with disabilities (CWDs) and without disabilities (CWODs) over the two years and determining predictors of the development of both groups of children. The participants were 61 pairs of CWDs and CWODs attending 53 inclusive preschool classrooms, in Ankara, Turkey. Data were collected on three occasions over two years, with fall and spring measurements with six months apart in the first year of the study and then again one year later, in the spring data point of the second year. The results showed that the developmental scores of the CWODs are higher than those of the CWDs at all measurement points, and the differences between the developmental scores of the two groups of children tended to close gradually in the second and third measurements. We found no significant longitudinal changes in problem behaviors and the student-teacher relationships of the CWDs and CWODs over the two years. In addition, the findings from canonical correlation analysis revealed that social skills provided the greatest contribution to the development of CWDs for the first and second measurements and the second-highest contribution in the third measurement.