The following definition has been adopted by the International Dyslexia Association
"Dyslexia is a neurologically based, often familial, disorder which interferes with the acquisition and processing of language. Varying in degrees of severity, it is manifested by difficulties in receptive and expressive language, including phonological processing in reading, writing, spelling, handwriting, and sometimes in arithmetic. Dyslexia is not a result of lack of motivation, sensory impairment, inadequate instructional or environmental opportunities, or other limiting conditions, but may occur together with these conditions, Although dyslexia is life-long, individuals with dyslexia frequently respond successfully to timely and appropriate intervention."