Classification of Learning Disabilities: An Evidence-Based Evaluation

Jack M. Fletcher, University of Texas; G. Reid Lyon, National Institutes of Health; Marcia Barnes, University of Toronto; Karla K. Stuebing, University of Texas; David J. Francis, University of Houston; Richard K. Olson, University of Colorado; Sally E. Shaywitz, Bennett A. Shaywitz, Yale University
Learning Disabilities Summit: Building a Foundation for the Future White Papers

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DEFINITIONS OF LEARNING DISABILITIES: IMPLICIT CLASSIFICATIONS MADE EXPLICIT

The evolution of definitions of LD can be traced to the turn of the last century and is closely linked to concepts of organically based behavioral disorders (Doris, 1993; Rutter, 1982; Satz & Fletcher, 1980). The concept of LD arose from observations of children who were hyperactive and impulsive, but for whom the cause of the disorder was not obvious. As these problems often occurred in children for whom there were a history or some other suspicion of a brain injury, it was often presumed that the cause of these unexpected behavior disorders was constitutional in origin. Thus, these children were described with terms such as organic driveness syndrome, minimal brain injury, and then in the 1960s, minimal brain dysfunction. The latter label, stemming from a meeting convened by the federal government in 1962 (Clements, 1966), recognized that many children with these behavioral difficulties also had difficulty mastering academic skills with associated processing difficulties despite adequate intelligence and opportunities to learn.

In a subsequent meeting in 1966 convened by the U.S. Office of Education (USOE; 1968), the concept of LD, as proposed by Kirk (1962), was formally defined and considered as inclusive of minimal brain dysfunction and related disorders. The notion of minimal brain dysfunction as a disorder not attributable to mental deficiency, sensory disorders, emotional disturbance, or cultural or economic disturbance was retained. Etiological terms were dropped and replaced by educational descriptors, although the notions of unexpectedness and the implicit attribution to constitutional factors were retained. Parental and professional advocacy efforts led to the provision of special education services through the 1969 Learning Disabilities Act. The legislative language in the 1969 Act later appeared in the Education for All Handicapped Children Act of 1975 (Public Law 94-142) and is now currently reflected in the 1997 reauthorization of the Individuals with Disabilities Education Act (IDEA). All these legislative proceedings used the 1968 definition of LD:

The term "specific learning disability" means a disorder in one or more of the basic psychological processes involved in understanding or in using language, spoken or written, which may manifest itself in an imperfect ability to listen, speak, read, write, spell, or to do mathematical calculations. The term includes such conditions as perceptual handicaps, brain injury, minimal brain dysfunction, dyslexia, and developmental aphasia. The term does not include children who have learning disabilities which are primarily the result of visual, hearing, or motor handicaps, or mental retardation, or emotional disturbance, or of environmental, cultural, or economic disadvantage. (USOE, 1968, p. 34)

After P.L. 94-142 was passed and federal funds became available, states were expected to identify children with LD. It quickly became apparent that states needed assistance with criteria for identification of LD, leading to publication of the Procedures for Evaluating Specific Learning Disabilities in the Federal Register (USOE, 1977). These procedures recommended that LD be defined as:

a severe discrepancy between achievement and intellectual ability in one or more of the areas: (1) oral expression; (2) listening comprehension; (3) written expression; (4) basic reading skill; (5) reading comprehension; (6) mathematics calculation; or (7) mathematic reasoning. The child may not be identified as having a specific learning disability if the discrepancy between ability and achievement is primarily the result of: (1) a visual, hearing, or motor handicap; (2) mental retardation; (3) emotional disturbance, or (4) environmental, cultural, or economic disadvantage. (USOE, 1977, p. G1082)

Although states vary considerably in the IQ and achievement criteria used to designate a child as LD, discrepancy is used in either the definition and/or criteria by virtually all states, with the use of an IQ test to establish "aptitude" equally common (Frankenberger & Fronzaglio, 1991; Mercer, Jordan, Alsop, & Mercer, 1996). Discrepancy is the only inclusionary criterion; all other criteria are exclusionary and indicate simply what LD is not. Although there was little research at the time validating classifications of LD based on IQ discrepancy, researchers, practitioners, and the public commonly assume that IQ discrepancy is a marker for a specific type of LD that is unexpected and categorically distinct from other forms of underachievement (Kavale & Forness, 2000; Mercer et al., 1996; Stanovich, 1993). These beliefs reflect the common observation of unexpected underachievement in children who seem bright and capable.

The reification of IQ discrepancy in public policy is clearly apparent in the definition of LD in the 1992 and 1997 reauthorizations of IDEA, which continued the 1968 definition and added the following criteria from the 1977 recommendations to states:

(a) A team may determine that a child has a specific learning disability if:

(1) The child does not achieve commensurate with his or her age and ability levels in one or more of the areas listed in paragraph (a) (2) of this section, when provided with learning experiences appropriate for the child's age and ability levels; and

(2) The team finds that a child has a severe discrepancy between achievement and intellectual ability in one or more of the following areas: (i) Oral expression; (ii) Listening comprehension; (iii) Written expression; (iv) Basic reading skill; (v) Reading comprehension; (vi) Mathematics calculation; or (vii) Mathematics reasoning. (U.S. Department of Education, 1999, p. 12457)

IQ discrepancy is clearly a prominent classification hypothesis. Other components of the federal definition also reflect classification hypotheses. Here we note the heterogeneity hypothesis, where LD is represented as seven different types of unexpected low achievement that may overlap. In addition, there is the exclusion hypothesis, which suggests that low achievement in LD is different from low achievement due to (a) mental deficiency and sensory disorders; (b) emotional disturbance; (c) social, economic, and cultural disadvantage; or (d) inadequate instruction. In the next sections, we review each of these classification hypotheses.

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