This paper is based on a study carried out in Great Britain on a national sample of 11,804 ten-year olds. The first section describes an attempt to pick out cases of "specific developmental dyslexia" (Critchley 1970), a constellation or syndrome of difficulties which some believe to be recognizable clinically. When specified criteria for dyslexia were used, 269 children qualified as dyslexic (2.28 percent of the sample). These included 223 boys and 46 girls, for a ratio of 4.51 to 1. Two possible difficulties in interpreting these data are discussed, and a defense is offered of the criteria used.Since some recent research papers report a gender ratio much nearer 1:1 (Shaywitz et al. 1990;Wadsworth et al. 1992;Lubs et al. 1993), those papers were examined for possible differences in procedure; it was found that the definition of dyslexia they used was "poor reading in relation to intelligence." We carried out a further analysis on our own data using the same criterion. Of the 494 children who qualified as dyslexic on the

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An experiment is reported in which dyslexics (on average ten-and-a-half years old) showed marked Stroop interference of a colour word on the naming of a colour. This interference was larger than that shown by control subjects matched for chronological age, but not larger than that experienced by a group of control subjects matched for reading age (about eight years old). Dyslexics show interference consistent with their reading age. It is hypothesized that the resources available to dyslexics for controlling automatic word reading are less than those for non-dyslexics of a similar chronological age.

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Seventy-two items testing vamous aspects of mathematics were given to 12,131 ten-year-old children. Criteria for specific developmental dyslexia (SDD) and for other groupings are specified. Despite the absence of differences in intelligence level, the mean score on the mathematics test for the dyslexics was not only lower than that of the normal achievers but lower also than that of underachievers believed not to be dyslexic.On some of the 72 items, there was little difference in percentage pass rate between the groups; on others, however, there were wide differences. On the basis of ratings carried out "blind" by a panel of experienced teachers of dyslexic children, and in the light of other considerations, some tentative suggestions are put forward as to what