Background: Children with developmental disabilities benefit from support in motor skills, sensory processing, cognitive development, and social skills. Mongolia has trained occupational therapists for a decade, with 37% specializing in pediatrics, but long-term therapy facilities remain limited. Aim: This study provides a case report on a child with developmental disabilities who received occupational therapy to evaluate improvements in sensory processing, social communication, and daily living skills. Materials and Methods: The study participants were purposively selected from children undergoing occupational therapy at the “Enerel” Child Development Center. Participant A is a 16-year-old male with hearing and speech impairments, as well as an intellectual disability. The initial assessment showed poor sensory processing and behavioral problems and communication difficulties. A tailored program incorporating sensory-based therapies, communication cards, and sign language was developed with caregiver collaboration. Occupational therapy was conducted five times weekly for 11 weeks. Pre and post test assessments included goal attainment scaling (GAS) and Sensory profile 2 (Child). Results: The participant showed improved communication using cards and sign language, better emotional regulation, enhanced sensory processing, and reduced hyperactivity to external stimuli. Goal Achievement (GAS) +2, meaning the goal was achieved better than expected and positive changes were found on the Sensory profile 2, with large effect sizes. Conclusion The study found that sensory- based occupational therapy and sign language training improved occupational performance and goal achievement in children with sensory, behavioral, and communication difficulties.