Validity

Given that only a very small proportion of dyslexic students are diagnosed prior to the age of 8, construct validity based on differences between dyslexics and non-dyslexics on the CoPS subtests would not be viable.

However, the predictive validity of CoPS is shown through the original longitudinal study which indicates that CoPS gives a highly satisfactory prediction of students who were later found to be experiencing literacy difficulties and dyslexia. The CoPS subtests produced significant correlations with reading development. Over 90% of students who subsequently were found to be experiencing significant literacy difficulties were successfully predicted on school entry by the CoPS subtests alone.