Parent training (PT) for parents of children with developmental disabilities (DDs) has recently been recommended in community settings in many countries, including Japan. Research has shown PT could improve parenting skills and mental health in parents as well as improve adaptive skills and reduce behavioral problems in children. Despite evidence concerning the beneficial effects of PT on both parents and children, there is a lack of evidence concerning the potential benefits of PT in real world settings. Moreover, no research has examined whether PT programs implemented in clinical settings have a similar impact on all parents of children with various type of DDs. The present pilot study aimed to examine whether positive changes occur similarly in parental mental health and in the adaptive skills of children with DDs as a result of PT, irrespective of the children's disability type. The study used data from 128 parents who had participated in a PT program in a clinical setting and data concerning 128 children aged 2-17 years with a wide range of DDs, namely autism spectrum disorder, intellectual disability, and other DDs, generated through parental reports and retrospectively assessed the impact of PT on parents and their children. Specifically, changes in parental mental health and the adaptive skills of children were analyzed. The PT program was designed to help parents teach their children adaptive skills at home using applied behavior analytic techniques. The results showed that the parents improved their mental health significantly after completing the PT, irrespective of their child's disability type. During the PT period, almost all the parents were able to implement several instructional tasks targeted toward their children; some children with DDs acquired several adaptive skills. However, these positive changes were not observed in all the parents and their children. These findings suggest that some parents and their children with DDs may benefit from the PT program in a clinical setting. Concurrently, these findings highlight the importance of providing sustained additional support in clinical settings to parents and their children with DDs.