Dyslexia is now acknowledged as a high incidence learning disability. It is estimated that 80% of all students with learning disabilities have documented reading problems. Estimates of the incidence of individuals with dyslexia in the population range from 5% to 17%. This broad range is due, in part, to the way dyslexia is defined in different contexts. If defined by inference-- those who show a gap of 11/2 standard deviations between actual reading achievement and that which might be expected on the basis of measured intelligence--the incidence is lower and the students are older. If defined on the basis of the phonological skills shown to support the acquisition of reading, the incidence is higher and includes students across the entire age range.

Until recently, identifying the cause of dyslexia had been elusive. It was recognized as occurring in families as early as the 1890s but only since the mid-1980s has research been able to document that dyslexia has a genetic basis. However, there is likely not a single dyslexia gene. Rather, it is probable that several genes, in combination, give rise to the condition.

Describing exactly what dyslexia is continues to be the subject of intensive and varied study. Dyslexia is a learning disability that appears to affect primarily the skills needed to interact with print but what, specifically, are the cognitive mechanisms that regulate these skills? Dyslexia is described as a specific language disability or impairment. In what ways is it like or unlike other language impairments? Is it a special case of language impairment or does it represent only a point on the continuum of language impairments?

In the context of this lack of clarity regarding what dyslexia is and what the condition might look like across the span of ages, preschool through adulthood, what must educators understand about approaches to identifying the condition and providing effective instructional supports? What might be the focus of professional training for teachers, reading specialists, school psychologists, and speech-language pathologists that will prepare them to effect a united and integrated approach to working with these students in school settings? And, how should schools be organized, in the interest of best practices, to specifically ensure an effective learning environment for those with dyslexia? What might be the role of public policy in encouraging and supporting advancement in all of these areas?

This issue of Topics on Language Disorders was conceptualized with a view toward addressing questions such as those noted above. Authors who have specific expertise in related areas were invited to prepare an original paper for this issue. The result will take the reader on a stimulating and thought-provoking journey through research, practice, and policy issues that serve to describe the current context in which we understand, question, and address the syndrome of dyslexia.

The first article, Dyslexia: A Generation of Inquiry, provides a brief overview of the research that has accumulated in a variety of fields over the past 28 years and forms the basic foundation of our current understanding about what dyslexia is, why it occurs, and how this knowledge is informing current educational practice. Sawyer traces the quest for a working definition of dyslexia from "word-blindness" to the phonological core deficit to a naming-speed deficit and the double-deficit hypothesis. The precursors of dyslexia are discussed from the standpoint of research into genetic inheritance, perceptual processing efficiency, and the formation and function of brain structures as these relate to processing printed language in various language cultures. The article concludes with a call for the development of effective literacy interventions that build on the current and emerging scientific knowledge base.

In the second article, The Dyslexia Spectrum: Continuities Between Reading, Speech, and Language Impairments, Snowling and Hayiou-Thomas address the question of dyslexia as a distinct disability or a disability that fits within the continuum of language impairments. The authors begin with a consideration of the cooccurrence of dyslexia and language impairments. They note that in one longitudinal study, 25% of children identified with an oral language impairment in kindergarten met the criteria for a diagnosis of dyslexia in grades 2, 4, and 8. The authors go on to develop the hypothesis that specific language impairments and dyslexia appear on the same continuum of risk for literacy difficulties and that risk involves language issues beyond phonology. In doing so, they draw upon and integrate research and theory in the areas of reading development, language development, the role of inheritance, and the influence of environment. They conclude with the proposal that effective intervention programs for dyslexia must address the fundamental language skills associated with semantic development as well as phonology.

In the third article, The Simple View of Reading: Assessment and Intervention, Roberts and Scott consider implications for assessment and intervention within the structure of a specific theoretical framework for reading. The Simple View gives prominence to the role of oral language comprehension in the development of reading. As Snowling and Hayiou-Thomas point out, students with dyslexia are also likely to experience a form of language impairment. For this reason, Roberts and Scott propose that speech-language professionals consider development of oral and written forms of language to arrive at an understanding of reading and reading difficulties at different stages from prereading among preschoolers to more skilled reading among adolescents. The authors provide an extensive discussion of theory and research that illustrates the interaction and codependence of oral with written language development. Implications for efficient assessment of reading difficulties and effective intervention practices are offered.

The fourth article, Dyslexia Friendly Schools in the UK, offers a perspective on how public policy can directly influence educational practice in public schools for special needs students, including those with dyslexia. Riddick describes the background, in the United Kingdom, leading up to the implementation of school curricula in the Swansea local education authority that supported the specific learning needs of students with dyslexia. Beginning in 1997, a thorough review of existing services followed by consultations and collaborations with parents, teachers, and the British Dyslexia Association resulted in adoption of a "dyslexia friendly policy." This policy emphasized the importance of training that included awareness of dyslexia and effective teaching techniques for all teachers. Various reports of student educational outcomes since 2001 suggest that implementation of the policy was successful. Interest is spreading to other local education authorities in the United Kingdom.

The final article addresses the influence of public policy on reading research and practice in the United States. Foorman and Nixon begin with an extensive discussion of the struggle for equal access to education, from Horace Mann's call for universal public education in 1837 to the struggles addressed in legal and legislative venues for racial equality and appropriate services to those with mental or physical or language differences. The authors then turn to a discussion of standards-based educational reform. The focus of this reform movement was shaped in large part by the research outcomes of programs sponsored by the National Institute for Child Health and Human Development (NICHD). These programs of research significantly influenced passage of the No Child Left Behind Act of 2001. The authors close with a promising report of progress in student achievement across the range of populations served. Foorman and Nixon provide a valuable framework for recognizing that public policy can and will shape the education enterprise, which, in turn, can shape the society it serves. However, change occurs slowly and rarely in a straight-line progression.

It is the collective hope of all contributors to this dedicated issue that you, the readers, will gain a deeper understanding of dyslexia, of the current context in which it is both researched and supported, and of the challenges that remain as we work to overcome the consequences of this complex syndrome.

Diane J. Sawyer, PhD

Issue Editor, Middle Tennessee State University, Murfreesboro