This paper presents a treatment study with a developmental dysgraphic girl, KM, and addresses the mechanisms by which orthographic learning of spelling rules might occur. Before treatment, KM's spelling of words and nonwords was impaired. Analyses of spelling errors indicated poor knowledge of sound-to-letter correspondences. Treatment focused on two spelling rules and was successful: spelling improved for both regular words and nonwords. Untrained words that included the training rules also improved, but later than nonwords and trained words. This delayed generalisation was explained through feedback mechanisms between orthographic lexicon and graphemic buffer.