Analyzes composition reading performance data from identical and fraternal twin pairs in order to test the hypothesis that genetic influences are more important as a cause of reading disability in girls than in boys. Provides little or no evidence for the hypothesis of greater genetic influence on reading difficulties in girls than in boys. (SC)

Fits spelling data from identical and fraternal twins to a basic multiple regression model. Finds that about 60% of the deficit of probands was due to heritable influences. Finds a nonsignificant sex difference. Suggests collaborative analyses of data from additional twin studies of reading disability to facilitate more rigorous tests. (RS)