This study evaluated whether core vocabulary intervention (CVT) improved single word speech accuracy, consistency and intelligibility in four 9-11-year-old children with profound sensori-neural deafness fitted with cochlear implants and/or digital hearing aids. Their speech was characterized by inconsistent production of different error forms for the same lexical item. The children received twice weekly therapy sessions for eight weeks. Fifty target words were drilled and changes in production assessed for accuracy and consistency. Generalization of consistency and accuracy was assessed on non-targeted words. There were four assessment points: six weeks pre-therapy; immediately before therapy; immediately following therapy and six weeks post-therapy. In addition, 10 unfamiliar listeners judged the intelligibility of audio recordings of the children's speech before and after therapy. The children's consistency and accuracy of single word production improved following CVT. Consistency generalized to untreated words. Sentence intelligibility ratings improved and more target words were identified after therapy. These case studies suggest that CVT merits further investigation as an effective intervention approach for deaf children, enhancing consistency, accuracy and intelligibility of speech.