Handwriting legibility reflects spelling difficulties in dyslexia but not in Developmental Coordination Disorder (DCD)

Purpose
Studies reporting spelling and handwriting deficits in dyslexia and DCD fail to consider comorbidity. Handwriting dysfluency has been linked to spelling difficulties in dyslexia but not in DCD, suggesting differential causes for dysfluency. In this study, we investigated another aspect of handwriting, legibility, and hypothesized that poorer legibility should be associated with spelling deficits in dyslexics (singular and comorbid), but not in DCD.

Method
Twenty-eight children with dyslexia (M age=9.3 years), 25 children with DCD (M age=9.2 years), 17 children with dyslexia and DCD (M age=9.4 years), and 83 controls (M age=9.2 years) completed a 62-word, graded sentence dictation task. Spelling and handwriting were scored independently. Scorers blind to spelling ability judged legibility on four dimensions: letter formation, letter spacing, word spacing, line alignment.

Results
Children with dyslexia (singular and comorbid) spelled less accurately than children with DCD and controls. On legibility, all disorder groups scored significantly lower on letter formation and letter spacing than controls. For word spacing and line alignment, children with DCD (singular and comorbid) received significantly lower ratings than controls, while dyslexics did not.

Conclusion
Dyslexics had lower spelling accuracy and legibility on dimensions related to spelling (letter formation and spacing) suggesting poor handwriting in dyslexia reflects spelling deficits. Children with DCD received low ratings on all dimensions of legibility – despite adequate spelling accuracy – indicating their handwriting impairments were not spelling specific. The comorbid group’s scores were no different to those with singular disorders, suggesting that their handwriting impairments reflect an additive profile of spelling and additional, DCD related, deficits.