Which aspects of reading ability show a ‘hump’ in their distribution?

Data from two studies on large samples of 7-, 11- and 13-year-old children were used to estimate the regression relationship between reading, spelling and maths achievement and IQ. Using these regression equations the number of children obtaining achievement scores more than two standard deviations below that expected were identified. It was found that there was a significant excess of underachievers for reading and spelling at 11 years but not for maths. This ‘hump’ was also found for the reading of non-words. It was concluded that the issue of whether such a ‘hump’ can be found is only a minor facet of the debate about the nature of reading failure, and that more direct studies of the processing of written text are likely to prove more decisive.