As defined by U. S. law, special education is: “specially designed instruction, at no cost to parents, to meet the unique needs of a child with a disability, including instruction conducted in the classroom, in the home, in hospitals and institutions, and other settings; and instruction in physical education” (Individuals with Disabilities Education Improvement Act, 2004) 20 U.S.C. § 1401 (29). The law also stipulates that students with disabilities are entitled to related services, as needed. Related services include such services as transportation, occupational and physical therapy, and psychological, counseling, speech/language pathology, audiology, and interpreting services.
SPECIALLY DESIGNED INSTRUCTION

For most students with disabilities, “specially designed instruction” is defined as involving intensive, relentless, structured, appropriately paced instruction, in small groups in which each student's progress is monitored frequently (Kauffman & Hallahan, 2005). According to Kauffman and Hallahan, all of these characteristics should usually be more evident in special education than is typically the case in general education. Intensive instruction translates into more teacher instructional time and more opportunities for students to respond to the instruction and more time to practice and review what they have learned. Relentless instruction involves repeating this sequence or parts of this sequence more often than is typically done with non-disabled students. Structured instruction refers to teachers being more directive, instituting more explicit rules, and providing more frequent consequences for appropriate or inappropriate behavior. The pace of the instruction in special education is tailored more to the needs of the student and is often slower, with teachers waiting for a longer period of time for a response after querying the student. Instruction in small groups facilitates the intensity, relentlessness, structured nature, and the individualized pace of instruction. Moreover, specially designed instruction means that a student's progress in learning is monitored frequently, often several times per week.

In addition to these general principles of instruction that apply to most students with disabilities, there are some that apply to specific categories of special education students. For example, for students with blindness or low vision, the “specialized designed instruction” may take the form of reading materials in Braille, large print, or audio recordings, and instruction in the use of a cane for mobility. For students who are deaf or hard of hearing, the instruction may involve sign language or hearing aids. Additionally, for students with emotional or behavioral disorders, instruction may require highly structured classrooms and teaching routines and use of functional behavioral assessment (FBA) and positive behavioral intervention and support (PBIS). FBA involves determining what factors help to set off and maintain inappropriate behaviors. And PBIS emphasizes “rewarding positive behavior, to make problem behavior less effective, efficient, and relevant and to make desired behavior more functional” (Hallahan, Kauffman, & Pullen, 2009, pp. 163–164).
SPECIAL EDUCATION CATEGORIES

Students served by special education fall into 13 disability categories. In order of prevalence they are learning disabilities, speech or language impairments, mental retardation, emotional disturbance, other health impairments (including attention deficit hyperactivity disorder), multiple disabilities, autism, orthopedic impairments, hearing impairments, developmental delay, visual impairments, traumatic brain injury, deaf-blindness. The federal government has provided definitions for each of these categories in order to give guidance to schools in finding students eligible for special education services.

Learning Disabilities. Students with learning disabilities are by far the largest category of special education, comprising between 5 and 6 percent of the school-age population and nearly half of all students identified for special education services. Although its historical roots can be traced back to work done in the 1800s in Europe (Halla-han & Mercer, 2002), learning disabilities as a condition and as a discipline was not formally recognized until the 1960s and 1970s. A major reason for the eventual recognition of learning disabilities as a condition warranting special education services came from parents and professionals who pointed out that there were many students who, although not scoring low enough on intelligence tests to qualify as mentally retarded, were nevertheless still displaying learning problems, especially in reading.

The federal definition of learning disabilities is as follows:
General—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 disorder may manifest itself in an imperfect ability to listen, think, speak, read, write, spell, or do mathematical calculations.).
Disorders Included—Such term includes such conditions as perceptual disabilities, brain injury, minimal brain dysfunction, dyslexia, and developmental aphasia.).
Disorders Not Included—Such term does not include a learning problem that is primarily the result of visual, hearing, or motor disabilities, of mental retardation, of emotional disturbance, or of environmental, cultural, or economic disadvantage (Individuals with Disabilities Education Act Amendments of 1997, Sec. 602(26), p. 13.).

Speech or Language Impairments. Speech impairments include disorders of articulation, fluency, and/or voice (American Speech-Language-Hearing Association, 1993). Articulation disorders often result from neuromuscular abnormalities resulting in omission, substitution, or distortion of speech sounds. Fluency refers to being able to produce smooth speech flow. Disorders of voice include such characteristics as abnormal pitch, loudness, or resonance.

Language impairments can include problems in production and/or comprehension that violate the rules of language pertaining to phonology, morphology, syntax, semantics, or pragmatics. Phonology rules govern how speech sounds are sequenced. Morphology refers to parts of words that indicate such factors as verb tense and plurals. Syntax involves word order that reflects proper grammar. Semantics refers to the meanings of words and sentences, and pragmatics involves using language for social purposes.

Mental Retardation. Most professionals use the definition of mental retardation provided by the American Association on Intellectual and Developmental Disabilities (AAIDD): “Mental retardation is a disability characterized by significant limitations both in intellectual functioning and in adaptive behavior as expressed in conceptual, social, and practical adaptive skills. This disability originates before age 18” (AAMR Ad Hoc Committee on Terminology and Classification, 2002, p. 1). The AAIDD considers the following five points as crucial to understanding the context of the definition:
Limitations in present functioning must be considered within the context of community environments typical of the individual's age peers and culture.
Valid assessment considers cultural and linguistic diversity as well as differences in communication, sensory, motor, and behavioral factors.
Within an individual, limitations often coexist with strengths.
An important purpose of describing limitations is to develop a profile of needed supports.
With appropriate personalized supports over a sustained period, the life functioning of the person with mental retardation (intellectual disability) generally will improve. (AAMR Ad Hoc Committee on Terminology and Classification, 2002, p. 1).

Emotional Disturbance. There is considerable controversy concerning the definition of emotional disturbance, which stems from the relatively subjective nature of the condition. In fact, even though the federal government uses the term emotionally disturbed, there are many professionals who prefer the term emotional or behavioral disorders because it more accurately conveys the socialization problems these students exhibit.

With respect to definition, many authorities agree on the following three features of emotional or behavioral disorders:
Behavior that goes to an extreme—that is not just slightly different from the usual;
A problem that is chronic—one that does not quickly disappear; and
Behavior that is unacceptable because of social or cultural expectations (Hallahan et al., 2009).

Other Health Impairments. According to the federal definition, other health impairments (OHIs) are medical conditions, such as asthma, diabetes, epilepsy, sickle cell anemia, which impair to such a degree that they adversely affect a student's educational performance. The key to the definition is that the condition must interfere with the student's educational performance. For example, not all students who have asthma have it to such a degree that it affects their ability to function in school.

Students with attention deficit hyperactivity disorder (ADHD) are also included in the federal government's category of OHI. The American Psychiatric Association (2000) recognizes three types of ADHD: (1) ADHD, predominantly inattentive type; (2) ADHD, predominantly hyperactive-impulsive type; (3) ADHD, combined type.

The reason behind the decision to place ADHD in the OHI category is an interesting lesson in disability advocacy and politics (Hallahan et al., 2009). In the late 1980s and early 1990s, parents of affected children lobbied intensely for ADHD as a new category of special education. Many surmise that the U. S. Department of Education was worried about creating yet another category, especially one that could potentially attract large numbers of students. Therefore, in 1991, they came up with the compromise of stating that students with ADHD could receive special education services if they were identified as having OHI, i.e., had a condition that interfered with their educational performance, thus leaving open the possibility that some students with ADHD would not meet the criteria of OHI because their educational performance was not adversely affected.

Multiple Disabilities. The multiple disabilities category consists of students who have two or more disabilities, “the combination of which causes such severe educational problems that they cannot be accommodated in special education programs solely for one of the impairments” (34 CFR, Sec. 300 [b][6]).

Autism. Many authorities in the early 2000s consider autism to be one of several similar conditions that fall on a spectrum, hence the term autism spectrum disorders. The conditions on the spectrum share impairments in three areas: (1) communication skills, (2) social interactions, and (3) repetitive and stereotyped patterns of behavior (Strock, 2004). Classic autism and Asperger syndrome are the most common conditions. Whereas students with autism have relatively severe deficits in all three areas plus severe cognitive deficits, those with Asperger syndrome generally have less severe deficits in all three areas, with their major problem lying in the area of social interactions and some having very high intelligence.

Orthopedic Impairments. Orthopedic impairments include physical disabilities of the muscles and/or bones that negatively affect school learning. Two examples are muscular dystrophy (a hereditary condition resulting in muscle fiber degeneration) and juvenile rheumatoid arthritis.

Hearing Impairments. Students with hearing impairments fall into two categories: those who are deaf and those who are hard of hearing. How one differentiates between the two depends on whether one adopts a physiological or an educational orientation. A physiologically based definition relies on the measurable degree of hearing loss, with those having an impairment of 90 decibels or greater being deaf (0 dB is the level at which the average person can hear the faintest sound). An educationally based definition focuses on the ability to process linguistic information, with deafness indicating that the person cannot process linguistic information through audition even with a hearing aid (Brill, MacNeil, & Newman, 1986).

Developmental Delay. For many infants and preschoolers, it is often difficult to determine whether they have a true disability or have a temporary delay in maturation. In addition, it is sometimes difficult to determine the exact nature of very young children's disability. For these reasons, professionals are often reluctant to make a clinical diagnosis and, instead, refer to them as having a developmental delay.

Visual Impairments. Like hearing impairments, visual impairments are divided into two groups based on severity: blindness and low vision. Additionally, like hearing impairments, these two groups are defined differently according to whether one uses a physiological versus an educational approach. A physiological orientation (also referred to as the legal definition because it is used to determine certain government benefits) relies on measurement of visual acuity and field of vision. Visual acuity of 20/200 (normal acuity is 20/20, being able to see at 20 feet what a person with normal vision sees at 20 feet) or less in the better eye, even with correction (e.g., eyeglasses), or visual field of less than 20 degrees qualifies an individual as legally blind. Those having visual acuity between 20/70 and 20/200 are referred to as having low vision or being partially sighted. The educational definition focuses on mode of reading, with those needing to use Braille being considered blind, and those who can read print, even with magnifying devices or large-print books, being considered as having low vision or being partially sighted.

Traumatic Brain Injury. In 1990, the federal government added students with traumatic brain injury (TBI) to the list of those eligible for special education services. This decision was in recognition of the fact that TBI occurs much more frequently than was previously thought. For example, estimates are that about one million children and adolescents receive head injuries each year, with 15,000 to 20,000 incurring lasting effects (Council for Exceptional Children, 2001). TBI refers to trauma to the brain caused by an external force that results in behavioral dysfunction. Such injuries can be open head injuries (i.e., penetrating head wounds) or closed head injuries (i.e., damage caused by internal compression or shearing motion inside the head) (Adelson & Kochanek, 1998).

Deaf-Blindness. Basically, students with deaf-blindness meet the educational definitions of both deafness and blindness. The vast majority of students with deaf-blindness also have one or more other disabilities, such as mental retardation. Deaf-blindness can result from (a) prenatal causes, such as rubella, (b) postnatal causes, such as meningitis, or (c) genetic/chromosomal syndromes