The application of cognitive neuropsychological theories to the design and implementation of treatment programmes remains relatively unexplored, especially in children. In addition, cognitive neuropsychological treatment programmes for dyslexia to date have focused on specific dyslexias such as phonological and surface dyslexia and have ignored the large subgroup of children with severe and multiple impairments of the reading system, those with mixed dyslexia. This study evaluates a sublexical treatment programme designed for a child with dyslexia of the mixed type. The treatment approach is based on sublexical treatment programmes that have been reported in cases of adult acquired dyslexia (Berndt and Mitchum, 1994; De Partz, 1986; Nickels, 1992). The focus of treatment is on nonword reading and includes training in grapheme parsing, grapheme-to-phoneme knowledge, and phoneme blending. Treatment outcome is measured through extensive pre- and post-treatment assessment of sublexical and lexical processing, semantics, and general phonology. The treatment design enables an objective assessment of treatment efficacy, stability of treatment effects over time and generalisability of the treatment to untreated stimuli and related language processes. The study illustrates the validity of the use of models and methods derived from work with adults with acquired impairments to paediatrics, and the usefulness of analytical models in cases of severe mixed dyslexia.