Previous spoken homophone treatment in aphasia found generalization to untreated homophones and interpreted this as evidence for shared phonological word form representations. Previous written treatment of non-homophones has attributed generalization to orthographic neighbours of treated items to feedback from graphemes to similarly spelled orthographic word forms. This feedback mechanism offers an alternative explanation for generalization found in treatment of spoken homophones. The aim of this study was to investigate the mechanism underpinning generalization (if any) from treatment of written homophones. To investigate this question a participant with acquired dysgraphia and impaired access to orthographic output representations undertook written spelling treatment. Generalization to untreated items with varying degrees of orthographic overlap was investigated. Three experimental sets included homographs (e.g., bank-bank), heterographs (e.g., sail-sale), and direct orthographic neighbours (e.g., bath-path). Treatment improved written picture naming of treated items. Generalization was limited to direct neighbours. Further investigation of generalization found that items with a greater number of close neighbours in the treated set showed greater generalization. This suggests that feedback from graphemes to orthographic word forms is the driving force of generalization. The lack of homograph generalization suggests homographs do not share a representation in the orthographic lexicon.