Electronic hearing aids were less successful in ensuring spoken language development in profoundly deaf children. Many years of intensive formal instruction by highly trained teachers was often required for deaf children todevelop the ability to make use of other sensory modalities to understand and produce speech. Their language development proceeded at about half the rate of hearing children, and they demonstrated average language delays of 4–5 years by the time they entered high school. The reported speech intelligibility of children with profound deafness was quite variable, averaging as low as 19% in some studies and as high as 76% in others.