nt.7 The majorcauses of language impairments are mentalretardation, hearing impairment, centralnervous system dysfunctions (generally inthe form of learning disabilities), and envi-ronmental factors such as lack of stimula-tion.8 Determining causes with precision inindividual cases is often not possible.Indeed, classifications based on causationhave not proven useful for remediation, andso professionals are generally advised to baseinterventions on an assessment of the indi-vidual student's language abilities.28Treatment by a language therapist gen-erally leads to improvement in functionalcommunication skills,29 although the treat-ment cannot usually be expected to eradi-cate the problem.Mental Retardation (MR)Eleven percent of IDEA-eligible studentshave mental retardation (MR).s The sever-ity of mental retardation is classified as mild(generally defined by an IQ test score ofbetween 50-55 and 70, accompanied bydeficits in adaptive behavior), moderate(IQ of 35-40 to 50-55), severe (IQ of20-25 to 35-40), or profound (IQ below20-25).31 Roughly 75% to 85% of thosewith mental retardation fall in the categoryof mild mental retardation (MMR).31,32 Inthis journal issue, the other three cate-gories are referred to collectively as severemental retardation.From an epidemiological viewpoint,using a cutoff of 50 IQ points to divide stu-dents into different classifications is arbi-trary, because students may show either mildor severe mental retardation as a result ofthe same diagnosis, such as Down's syn-drome. As a group, however, students withsevere mental retardation are more likely toalso show signs of serious conditions withneurological complications, such as Down'ssyndrome, cerebral palsy, epilepsy, hearingimpairment, visual impairment, and otherstructural, chromosomal, or metabolic birthdefects affecting the central nervous system.In a study of 458 students with mental retar-dation in Atlanta," two-thirds of the studentswith severe MR, but less than 20% of the stu-dents with MMR, were known to have anoth-er neurological condition. Moreover, thestudents with severe mental retardation weremore likely to have multiple neurologicalconditions.Nationally, African-American studentsare more than twice as likely as whites tobe diagnosed as having MMR. (See thearticle by Reschly in this journal issue.)Researchers have some understanding,though far from complete, of the reasonsfor this disproportionate representation.Causes most commonly proposed arepovertyl6 and cultural bias." Recent impor-tant research concludes that poverty is amajor cause of disproportionate African-American representation within the MMRcategory, but that poverty does not explainthe differences at the mildest levels of me

8 THE FUTURE OF CHILDREN - SPRING 1996Despite their prevalence, learning disabil-ities are poorly defined or understood.Learning disabilities are identified by profes-sionals in many fields, including pediatrics,psychology, neurology, and audiology.Although a coalition of professional and par-ent organizations has agreed upon a broadand complex definition of LD,21 there are nouniversally accepted, validated tests or diag-nostic criteria to determine the presence orabsence of learning disabilities. Someobservers argue that the IDEA's requirementof multidisciplinary evaluations increases thelikelihood of an LD diagnosis because a stu-dent may meet the criteria established by oneprofessional discipline but not another.=Learning disabilities are most commonlydiagnosed on the basis of a notable discrep-ancy between the student's academicachievement and ability to learn. In otherwords, the student has reasonable intelli-gence and adequate opportunity to learnbut performs poorly for unknown reasons.Ability to learn is usually measured by intelli-gence quotient (IQ), and the discrepancybetween ability and achievement must besubstantial. Specific standards are set by indi-vidual states, but the American PsychiatricAssociation suggests a discrepancy of eithertwo standard deviations or one standarddeviation plus other factors such as motor,sensory, or language differences, which arebelieved to have artificially depressed thestudent's IQ

Ethnicity and DisabilityIt has long been noted that AfricanAmericans are disproportionately represent-ed in special education. At the same time,Hispanics are nominally underrepresentedin most categories of special education. (Seethe article by Reschly in this journal issue.)While it is common for special educators tobe accused of overidentification of minoritychildren, attributing some identifications tocultural bias, Wagner found higher inci-dence among minorities of deafness, blind-ness, and other disabilities measured byaccepted, objective criteria. In her statisticalanalysis of a large sample, poverty played amajor role in this overrepresentation.17 Themajority of the disproportionate representa-tion of African-American students in specialeducation is within the category of mildmental retardation. Disproportionate repre-sentation is discussed by Reschly in connec-tion with mental retardation.Eligibility and EntitlementProcessesStudents who may have a disability are iden-tified and referred for evaluation by theirclassroom teachers or, more rarely, by theirparents or pediatricians.s8 Once referred,students are entitled to a multidisciplinaryevaluation provided by specialists compe-tent in each area of suspected disability.9 Ifa student is found to have a disability and toneed special services, then he or she is enti-tled to services under the IDEA. Once eligi-bility is determined, the school develops anindividualized education program (IEP) lay-ing out goals for the student, proposedplacement, and services to be provided bythe school district. Parental consent isrequired before a student can be evaluated,services provided, or the student's place-ment chang

Although identifying a student as "dis-abled" entitles him or her to special educa-tion services, a potentially large expense,school districts nationally have identified alarger proportion of their student body eachyear as having a disability. Many factors con-tribute to this increase.First, funding incentives in most statesencourage school districts to label studentsas disabled. Services delivered to studentswith a "disability" label are likely to be eitherpartly or fully reimbursed by the state,whereas the same services given to studentswithout a recognized disability are

have real, persistent, and substantial individ-ual differences and educational needs thatregular education has been unable toaccommodate. These individual differencesvary widely, from medical conditions such ascerebral palsy, to dyslexia, to pervasive andchronic maladaptive patterns of behavior

The IDEA governs the educational rights of individuals from birth to age21, though only students in elementary and secondary school are addressedin this journal issu

s. Only since a federal court case in 19722 and the passage offederal legislation in 19753 have all states been mandated to provide a free,appropriate public education to all students with disabilities.Today, as Parrish and Chambers point out in this journal issue, specialeducation for students with disabilities is the largest categorical program inpublic schools, costing an estimated $32 billi