Background: Autism spectrum disorder and cerebral palsy are prevalent neurodevelopmental disorders. Autistic individuals or individuals with cerebral palsy often struggle with sensory processing that further impacts movement execution. Immersive virtual reality (VR) is a promising assessment and intervention modality to promote motor learning in these populations because it supports natural interaction, enables real-time eye and hand movement tracking, integrates with external sensors, allows for real-time parameter control, and provides vivid, feedback-rich environments that may enhance motivation and engagement. These features facilitate a comprehensive understanding of performance and progress, enabling individualized adjustments to meet specific therapeutic goals. However, there is limited evidence exploring how visuomotor features in VR interact with sensory processing difficulties in autistic individuals or individuals with cerebral palsy. This dissertation addresses this gap in knowledge by evaluating and comparing visuomotor integration processes, affective measures, and motor learning in VR versus flatscreen environments and the physical environment in autistic individuals, individuals with cerebral palsy, non-autistic adults, and typically developing children. Methods: Autistic adults and children with cerebral palsy were recruited. Visuospatial accuracy and visuomotor integration in VR were evaluated for autistic adults and compared to the physical environment using a special estimation task and an overhand throwing task (Chapter 2). The impact of VR on affective factors (motivation, engagement, and cognitive load), motor skill acquisition, retention, and transfer to a flatscreen environment and to a comparable real-world task was evaluated in typically developing children using a novel postural control and reach-to-touch task (Chapter 3). The use of VR as a clinical assessment tool for visuomotor integration in children with cerebral palsy was evaluated in a clinical setting using a gross motor task (reach-to-touch), and the results were compared to the gold-standard paper-and-pencil (Beery-Buktenica) visuomotor integration test (Chapter 4). Results: Visuospatial accuracy and visuomotor performance were reduced in VR for autistic and non-autistic adults. Both groups exhibited lower throwing accuracy in VR and more active scanning of the entire environment in VR, rather than focusing on the task-relevant areas. Additionally, they demonstrated different visuomotor integration patterns during the execution of throwing movement in VR. Reducing visual clutter in VR improved eye movement measures and decreased performance errors in autistic adults. Motor skill acquisition in VR led to the highest motivation and performance gain for typically developing children but did not provide additional advantages for retention, transfer to a flatscreen environment, and to a real-world equivalent task. For children with cerebral palsy, visuomotor performance was also reduced in VR, as indicated by reduced reach-to-touch accuracy and slower movement execution in VR. Incorporating additional depth cues reduced hand movement endpoint errors during reach-to-touch tasks in children with cerebral palsy. Conclusions: This dissertation investigated the impact of VR on visuospatial accuracy, visuomotor integration, and motor learning for autistic adults, typically developing children, and children with cerebral palsy. The findings revealed reduced visuospatial accuracy and different visuomotor integration process in VR compared to the identical tasks in the physical environment, and highlighted individual visual perception, visuomotor integration, affective factors and environmental factors that contribute to motor performance and motor learning outcomes in VR. However, results support the potential of immersive VR as a motor rehabilitation intervention. In particular, adjusting visual information in VR can support visual behavior and improve performance. Acquiring a new skill in immersive VR boosted motivation during motor skill acquisition in typically developing children and enabled the greatest performance gains compared to non-immersive flatscreen systems and the physical environment. These findings contribute to the fundamental understanding of visuomotor performance and motor learning in VR for individuals with autism and cerebral palsy. They encourage further research to evaluate the impact of VR on other aspects of visual perception such as motion perception, and to explore individualized content adaptations to support visuomotor integration and motor (re)learning aligned with individual motor rehabilitation goals. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]