Children and adults classified as learning disabled (LD) are individuals of normal intelligence who suffer mental information processing difficulties that influence their academic performance. Several types are referred to as LD, reflecting a heterogeneous group of individuals with intrinsic disorders that are manifested by specific difficulties in the acquisition and use of listening, speaking, reading, writing, reasoning, or mathematical abilities (Hammill, 1990). These definitions assume that the learning difficulties of such individuals are as follows:
- Not due to poor instruction, but to specific psychological processing problems (e.g., remembering the association between sounds and letters) deriving from a neurological, constitutional, and/or biological base;
- Not due to inadequate opportunity to learn, general intelligence, or to significant physical or emotional disorders;
- Not manifested in all aspects of learning but specific to an academic behavior, for example, deficits in reading, but not arithmetic.
In several LD studies, children and adults with LD are operationally defined as having general IQ scores above 85 and standardized reading and/or math scores below the 25th percentile. The incidence of children with LD is conservatively estimated to reflect 2% of the public school population. LD is the largest category of children served in special education.
Problems of definition have severely affected the field of LD as a discipline because considerable latitude exists among psychologists in defining LD. This latitude is influenced by social/political trends as well as non-operational definitions of LD. The field is further exacerbated by the fact that the number of individuals classified with LD increased dramatically between 1985 and the early 2000s.
One impediment to advances in the field is unresolved issues related to discrepancy and another related to the importance of IQ. Traditionally, studies of children with LD have relied primarily on uncovering a significant discrepancy between achievement in a particular academic domain and general intellectual ability. The implicit assumption for using discrepancy scores is that individuals who experience reading, writing, and/or math difficulties, unaccompanied by a low IQ, are distinct in cognitive processing from slow or low achievers (e.g., Fletcher et al., 1992). This assumption is equivocal (e.g., Hoskyn & Swanson, 2000; Stuebing et al., 2002). Many studies have compared LD children with reading disabilities (RD, i.e., children with discrepancies between IQ and reading) with non-discrepancy defined poor readers (i.e., children whose IQ scores are in the same low range as their reading scores) and found that these groups are more similar in mental processing difficulties than different (Hoskyn & Swanson, 2000; Stuebing et al., 2002). As a result, some researchers have suggested dropping the requirement of average intelligence, in favor of a view by which children with reading problems are best conceptualized as existing at the extreme end of a continuum from poor to good readers (Stanovich & Siegel, 1994).
With the Individuals with Disabilities Education Improvement Act (IDEA, 2004), the United States federal government recognized potential problems with the IQ-discrepancy method by formally stating that the IQ-achievement discrepancy method was not necessary for LD diagnosis. To facilitate identifying children with LD, three criteria were added to the law:
States are not required to use a severe discrepancy between intellectual ability and achievement.
The procedure must include a process in which the children's response to scientifically based research interventions is considered in the assessment process.
States are permitted to use alternative research-based procedure to determine a specific learning disability.
Changes in the law were based on the assumption that IQ levels in children with low reading scores were irrelevant to a valid classification of LD. One alternative approach is referred to as response to instruction (RTI).
The goal of RTI is to monitor the intensity of instruction and make systematic changes in the instructional context as a function of a student's overt performance. This is done by considering various tiers of instructional intensity. As of 2008, RTI as an assessment approach for defining LD has aweak experimental base. There have been nocontrolled studies randomly assigning children seriously at risk for LD to assessment and/or delivery models (e.g., tiered instruction vs. special education (resource room placement) that have measured outcomes on key variables (e.g., overidentification, stability of classification, academic and cognitive growth in response to treatment). In addition, different states and school districts variously interpret how RTI should be implemented further undermining any uniformity between the science of instruction and assessment of children at risk for LD.
The validity of using discrepancy as a basis for defining LD, however, is not easily confirmed. Hoskyn and Swanson (2000) found in a synthesis of the literature that although children with RD and poor readers share some deficits in phonological processing and automatic-ity (naming speed), the RD group's performance was superior to poor readers on measures of syntactical knowledge, lexical knowledge, and spatial ability (also see Fuchs et al., 2000). Another finding was that cognitive differences between the two ability groups are more obvious in the earlier grades. Perhaps more important, a meta-analysis of the intervention literature (Swanson & Hoskyn, 1998) found that students with LD and low achievers differ in the magnitude of their responsiveness to treatment. Review of several intervention studies suggests that students who have low reading scores (25th percentile) but average IQ scores were less responsive to interventions than children whose reading and IQ scores were in the same low range (25th percentile) (also see Swanson & Hoskyn, 1998, pp. 300-301).
Typically, researchers who study the processing difficulties of children with LD do not use discrepancy criteria (Swanson, 1989). The majority of researchers rely on cut off scores on standardized measures above a certain criterion of general intelligence measures (e.g., standard score > 85) and cut-off scores below a certain criterion (e.g., standard score < 85) on primary academic domains (e.g., reading and mathematics).
Because of the heterogeneity of individuals classified as LD, several subtypes have been discussed in the literature. However, some subtypes have been considered invalid because (a) the particular subtypes do not respond differently to instructional programs when compared to other subtypes, and/or (b) the skills deficient in a particular subtype is not relevant to the academic areas important in the school context.
There are two subtypes, however, with extensive research that are relevant to the school context: reading disabilities and mathematical disabilities. These subtypes are defined by standardized (normed referenced) and reliable measures of intelligence and achievement. The most commonly used intelligence tests are from the Wechsler measures and common achievement tests that include measures of word recognition or identification (i.e., Wide Range Achievement Test, Woodcock Reading Mastery Test, Kaufman Test of Educational Achievement, Peabody Individual Test) and arithmetic calculation (all the aforementioned tests and the Key Math Diagnostic Test). In general, individuals with IQ scores equal to or above a Full Scale IQ score of 85 and reading subtest scores equal to below the 25th percentile and/or arithmetic subtest score equal to or below the 25th percentile constitute two high incidence disorders within LD: reading disabilities and math disabilities.
In terms of reading disabilities, Siegel (1989; 2003) argues that fundamental to evaluating reading disabilities is focus on word recognition measures because they capture more basic cognitive processes and responses than reading comprehension. Her research shows that difficulties in phonological processing are fundamental problems for children with reading disabilities, a problem that continues to adulthood. She also indicates that there is no evidence to suggest that development of decoding skills is a result of a specific instruction in graphemephoneme conversion rules. Her work and the work of others find that there are three processes critical in analysis of reading disabilities: those related to phonological processing (ability to segment sounds), syntactical processing, and working memory (combination of transient memory and long term memory).
In terms of math disabilities, Geary (1993, 2003) finds that children with arithmetic problems do not necessarily differ from academically normal peers in terms of the types of strategies used to solve simple arithmetic problems. Differences, however, are found in the percentage of retrieval and counting errors. Children with math disabilities have long-term memory representations of arithmetic facts that are not correct. He provides taxonomy of three general subtypes of mathematical disability: those related to procedural errors, those related to semantic memory, and those with visual/spatial difficulties. He indicates that the ability to retrieve basic arithmetic facts from long-term memory is a defining feature of math disabilities.
The term learning disabilities was first introduced in a speech by Samuel Kirk delivered in 1963 at Chicago Conference on Children with Perceptual Handicaps. Clinical studies prior to 1963 showed that a group of children who suffered perceptual, memory, and attention difficulties related to their poor academic performance but who were not intellectually retarded, were not being adequately served in the educational context.
Regarding the history of LD as a field, Wiederholt (1974) indicated that its unique focus was on identifying and remediating specific psychological processing difficulties. Popular intervention approaches during the 1960s and 1970s focused on visual-motor, auditory sequencing, or visual perception training exercises. Several criticisms were directed at these particular interventions on methodological and theoretical grounds.
By the late 1970s, dissatisfaction was expressed with a processing orientation to remediation of learning disabilities and with the influence of federal regulations in the U.S. (Public Law 94-142) remediation programs focused on basic skills such as reading and mathematics. The focus on basic skills rather than psychological processes was called direct instruction. The mid 1980s witnessed a shift from the more remedial-academic approach of teaching to instruction that included both basic skills and cognitive strategies (ways to better learn new information and efficiently access information from long-term memory). Children with LD were viewed as experiencing difficulty in regulating their learning performance. An instructional emphasis was placed on teaching students to check, plan, monitor, test, revise, and evaluate their learning during their attempts to learn or solve problems.
The early 1990s witnessed a resurgence of direct instruction intervention studies, primarily influenced by reading research, which suggested that a primary focus of intervention should be directed to phonological skills. The rationale was that because a large majority of children with learning disabilities suffer problems in reading, some of these children's reading problems are exacerbated because of lack of systematic instruction in processes related to phonological awareness (the ability to hear and manipulate sounds in words and understand the sound structure of language). This view gave rise to several interventions which emphasized phonics instruction and intense individual one-to-one tutoring to improve children's phonological awareness of word structures and sequences.
Some experimental research shows that children with LD can be assessed and significant gains can be made in academic performance as a function of treatment (see Vellutino et al., 2004). However, considerable evidence suggests that some children with normal intelligence when exposed to the best instructional condition fail to efficiently master skills in reading, mathematic, and/or writing (e.g., Fuchs & Fuchs, 1998; Torgesen, 2000). Some literature suggests that LD individuals are less responsive than generally poor readers to intervention (e.g., Swanson & Hoskyn, 1998) and these academic problems persist into adulthood (e.g., Ransby & Swan-son, 2003). Further, these difficulties in academic mastery reflect fundamental deficits in processing, such as phonological processing and working memory (Swanson & Siegel, 2001).
Swanson, Hoskyn and Lee (1999) provided a comprehensive analysis of the experimental intervention literature on LD. Their synthesis of methodologically sound studies (those with well-defined control groups and clearly identified LD samples) found that positive outcomes in remediating academic behaviors (e.g., reading, writing, mathematics) were directly related to a combination of direct and strategy instructional models. These models included a graduated sequence of steps with multiple opportunities for overlearning the content and skills, cumulative review routines, mass practice, and teaching of all component skills to a level that shows mastery. The interventions involved (a) teaching a few concepts and strategies well rather than superficially, (b) teaching students to monitor their performance, (c) teaching students when and where to use the strategy in order to enhance generalization, (d) teaching strategies as an integrated part of an existing curriculum, and (e) providing teaching that includes a great deal of supervised student feedback and practice.
Swanson (2000) found that two critical instructional components underlie successful instructional interventions for children with LD. One component was explicit practice that includes activities related to distributed review and practice, repeated practice, sequenced reviews, daily feedback, and/or weekly reviews. The other component was advanced organizers, and these studies included activities (a) directing children to focus on specific material or information prior to instruction, (b) directing children about task concepts or events before beginning, and/or (c) the teacher stating objectives of instruction.
See also:Attention-Deficit/Hyperactivity Disorder (ADHD), Direct Instruction, Individualized Education Program (IEP), Learning and Teaching Mathematics, Learning and Teaching Reading, Meta-Analysis, Special Education, Strategies Instruction
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