This study compared the developmental gains of preschool children with disabilities (CWD) and children without disabilities (CWOD) during a year they spent in preschools and examined the predictors of development in both groups (60 CWD and 57 CWOD) of children. Data on the social skills, problem behaviors, school adjustment level, student-teacher relationship, and the developmental functions of children were collected from the mothers and teachers, whereas trained assistants assessed the development of children. Analyses indicated that although all of the children made developmental gains, the psychomotor, language, and socioemotional developmental gains were greater for CWD than those for CWOD. Furthermore, social skills and school adjustment levels were found to be significant predictors of developmental gains of CWD. Implications of these findings were discussed in terms of the content of preschool curriculums, teacher preparedness related to inclusive practices, and the importance of and teaching social skills to CWD.