Prevalence of Learning Disabilities

It should be noted that prevalence figures can vary widely between states and within a state, depending on the stringency of the method used to determine eligibility. For example,

Kentucky reports the lowest prevalence figure (2.9%) and Massachusetts the highest (7.35%). A study completed in Michigan compared the learning disabilities eligibility criteria and procedures for identification across the 57 regional education service agencies in the state (RESA). The results indicated that 21% of the RESAs had no written eligibility criteria or policies, the length of the written policies varied from one sentence to 112 pages, and the severe discrepancy formula score varied from 15 to 30 standard score points! It is possible for a student to move a few miles to the next school district and no longer be considered to have a learning disability. (Smith, Pollaway, Patton, & Dowdy, 2004, p. 164)

Studies show that learning disabilities do not fall evenly across racial and ethnic groups. For instance, in 2001, 1% of white children and 2.6% of non-Hispanic black children were receiving LD-related special education services. The same studies suggest that this has to do with economic status and not ethnic background. Learning disabilities are not caused by economic disadvantage, but in low-income communities there is increased risk of exposure to harmful toxins (lead, tobacco, alcohol, etc.) at early stages of development.

Boys outnumber girls by about three to one in the LD category. Some researchers have suggested that the prevalence of learning disabilities among males is due to their biological vulnerability. However, others have suggested that "the higher prevalence of learning disabilities among males may be due to referral bias." They suggest that "academic difficulties are no more prevalent among boys than girls, but that boys are more likely to be referred for special education when they do have academic problems because of other behaviors, such as hyperactivity. Research on this issue is mixed" (Hallahan & Kauffman, 2003, p. 155).

The prevalence of LD also varies by age. Not surprisingly, the number of students receiving special education services increases steadily between the ages of 6 and 9. The bulk of students served (42%), however, are between the ages of 10 and 13, with a sharp decrease observed for individuals between 16 and 21 years of age (U.S. Department of Education, 2000; cited in Gargiulio, 2004, p. 210).

The true prevalence of learning disabilities is subject to much dispute because of the lack of a standard definition of LD and the absence of objective diagnostic criteria. Some researchers have argued that the currently recognized 5% prevalence rate is excessive and is based on vague definitions, leading to inaccurate identification. On the other hand, research efforts to identify objective early indicators of LD in basic reading skills have concluded that virtually all children scoring below the 25th percentile on standardized reading tests can meet the criteria for having a reading disorder. While less is known about LD in written expression, researchers estimate its true prevalence at between 8% and 15% of the school population. Research also indicates that approximately 6% of the school population has difficulties in mathematics which cannot be attributed to low intelligence, sensory deficits, or economic deprivation.

Finally, the dramatic increase in the number of students identified with LD is getting mixed reviews from learning professionals. For some, the increase is alarming, raising concerns that students are being overidentified. By contrast, other experts believe that the increased prevalence is reasonable, considering the newness of the field (Fuchs et al., 2001; cited in Turnbull et al., 2004).