Do Spelling and Vocabulary Improve Classification Accuracy of Children's Reading Difficulties Over and Above Word Reading?

It is widely recognized that individuals with dyslexia have difficulties with word reading and spelling, and individuals with reading comprehension difficulties have low vocabulary knowledge. However, little is known about the extent to which spelling and vocabulary are informative of reading difficulties. In the present study, we investigated whether information on students' spelling and vocabulary in kindergarten increases the precision of identifying students with reading difficulties, using longitudinal data from kindergarten to Grade 2. The sample was composed of 247 kindergartners (55% boys; 56% White children, 35% African American children, and 5% mixed-race children; 72% from low SES) who were followed to Grade 2. Spelling improved the accuracy of identifying students who experienced word reading difficulties in kindergarten and Grade 1. In contrast, vocabulary did not improve the accuracy of identifying students with reading difficulties over and above word reading and spelling. These results indicate the importance and utility of including spelling, in addition to word reading, as an integral part of accurately identifying children with reading difficulties as early as kindergarten. In addition, although vocabulary did not contribute additional predictive power, it is likely to exert its influence at a later phase of reading development.