Developmental trends in cognitive skills for children diagnosed as autistic and schizophrenic

102 children whose histories included a diagnosis of infantile autism or childhood schizophrenia were followed longitudinally to assess cognitive developmental trends. Despite some sample attrition, administration of a test battery of 5 language skill measures and 2 perception skill measures during 5 test periods over 4 years yielded 336 usable test batteries. After all tests had been administered, diagnosis of subjects for autism and schizophrenia using developmental histories and behavioral observations drawn at the time of first test-battery administration showed 111 test batteries on 33 children diagnosed as autistic, and 100 test batteries on 27 children diagnosed as schizophrenic. Comparisons of age and test score correlations, comparisons of cross-sequential means, and trends for means for diagnostic subgroups and normal controls suggest developmental delay for all skills at all ages for both autistic and schizophrenic children. Findings also suggest a trend for steady prepubertal cognitive skill development, followed by a postpubertal decline in skills for both diagnostic groups.