Mental development of adults with Down syndrome.

Measures of cognitive, verbal, and functional performance obtained at widely separated time periods were examined for adults with Down syndrome. Comparisons of first and last test profiles for Raven Coloured Progressive Matrices, Peabody Picture Vocabulary Test, and Adaptive Functioning Index (Social Education) Test all demonstrated significant increases over a mean time span of 5 years. These increases could not be attributed to year of entry into program, history of institutionalization, or age of the individuals. The findings indicate that mental development of adults with Down syndrome continues well into the third and fourth decade of life.