And Miles to Go...:
State SLD Requirements
and Authoritative Recommendations

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Questioning the Ability-Achievement Discrepancy

Challenges to the ability-achievement discrepancy criterion appeared occasionally from 1975 to 1995 (e.g., Cruickshank, 1979, Siegel, 1989). It was not until the late 1990s that the criticisms were sufficiently cogent and persuasive that the broader professional community took notice and professional associations began to consider alternatives. Multiple researchers have questioned the severe discrepancy criteria due to its poor or undemonstrated reliability and validity (Fletcher, et al., 1998; Lyon, 1996; Lyon, et al., 2001; Siegel, 1989, 2003; Stage, Abbot, Jenkins, & Berninger, 2003; Stuebing et al., 2002; Vellutino, Scanlon, & Lyon, 2000). Some representative conclusions appear below.

"In short, neither the phenotypic nor the genotypic indicators of poor reading are correlated in any reliable way with IQ discrepancy. .... Thus, the basic assumption that underlies decades of classification in research and educational practice regarding reading disabilities is becoming increasingly untenable. (Stanovich & Siegel, 1994).

"Classifications of children as discrepant versus low-achievement lack discriminative validity. .... However, because children can be validly identified on the basis of a low-achievement definition, it simply is not necessary to use an IQ test to identify children as learning disabled." (Fletcher, et al., 1998, p. 200)

The fundamental criticism of the ability-achievement discrepancy is that it does not establish a group of students with unique needs (Fletcher, et al, 2002). In fact, poor readers with IQs commensurate with their reading levels (non-discrepant) and poor readers with higher IQs (discrepant) have the same needs and respond to the same kind of instruction with comparable results. From this conclusion it follows that separating groups of poor readers into lower and higher IQ groups has dubious validity and likely deprives many students of the focused reading interventions that they need.

The underlying theoretical rationale for the ability-achievement discrepancy depends to a large degree on the validity of the two group hypothesis of low reading achievement. Rutter and Yule (1975) published data interpreted as revealing two groups of poor readers, one with IQs consistent with reading achievement called generally reading backward and another with IQs higher than reading achievement called specific reading retarded. Although the two groups had the common characteristic of very low reading achievement, the Rutter and Yule's specific reading retarded group differed from the general reading backward on several characteristics including educational prognosis. Rutter and Yule's two group hypothesis, particularly the reported better prognosis for the specific reading retarded group, is believed by some to have been influential on establishing the severe discrepancy in the Federal SLD classification criteria (Steubing, et al., 2002, p. 473).

The two group hypothesis, although attractive to persons defending traditional conceptions of SLD (Kavale, 2002; Scruggs & Mastropieri, 2002), has received equivocal support from some researchers and outright rejection from others over the last 25 years (Fletcher, et al., 2002; Francis, Shaywitz, Stuebing, Shaywitz, & Fletcher, 1996; Shaywitz, Escobar, Shaywitz, Fletcher, & Makuch, 1992; Stage et al., 2003; Stanovich & Siegel, 1994; Steubing, et al, 2002; Vellutino, et al., 2000). It appears that the two group hypothesis is supported only under limited conditions involving, among other things, a general reading backwardness group that has multiple problems such as mild MR and sensory deficits. Students with these characteristics are explicitly excluded in nearly all current SLD classification criteria potentially rendering much of the two group hypothesis irrelevant to groups of students with SLD. Interested readers are referred to an especially good account of the evidence on the two group hypothesis in Steubing et al. (2002).

Perhaps the most devastating criticism of the severe discrepancy classification method is that it delays treatment to later grades when the child is farther behind peers and effective interventions are more difficult to implement (Fletcher, et al, 1998; Stage et al., 2003; Stuebing, et al., 2002). For technical reasons, it is very difficult for poor readers to meet the discrepancy criterion until grade 3 or 4, although reading difficulties that lead to later diagnoses of SLD due to low reading usually are apparent in late kindergarten and 1st grade. The "wait to fail" effect conforms with the practical experience of many general and special educators who are familiar with the pattern of children experiencing reading difficulties in first grade, being referred for a full and individual evaluation, found not to be eligible for classification as SLD and placement in special education. This pattern often is repeated in 2nd and 3rd grade with the same results. Intensive remedial instruction in reading often is delayed until reading problems are much more difficult to address successfully.

School expectations change significantly at middle and upper grades where, increasingly, children are expected to read to learn while in the K-3rd grade period the main task is learning to read. Delaying intensive reading interventions to 3rd grade or later confers an enormous disadvantage that might be mitigated if effective reading interventions occurred earlier when reading problems are first apparent.

There is an irony in the ability-achievement discrepancy discussion. The myriad issues with the reliability and validity of this criterion likely would not have produced a consensus to change. Unfortunately, those deficiencies probably would have been tolerated for some time to come, perhaps rationalized by the belief the ability-achievement discrepancy, although flawed, was the best available solution to a complex problem. The pivotal issue has become harm to children. The ability-achievement discrepancy delays treatment to a point where interventions are less effective and children suffer the profound consequences of poor reading competencies.

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