Intellectual disability (ID), a condition previously known as mental retardation, is defined as a disability characterized by significant limitations both in intellectual functioning and in adaptive behavior as expressed in conceptual, social, and practical adaptive skills and that the basis for the disability has been present prior to age 18 (AAIDD, 2002). This condition affects about 1% of population (Bello, Goharpey, Crewther & Crewther, 2008), and has historically been defined as an intelligence quotient (IQ) score of less than 70 (Schalock & Luckasson, 2004). In recent decades, the definition of ID has been revised, which now includes both a measure of intellectual functioning and an indication of individuals' adaptive behavior in their environment.
Intelligence refers to individual's overall mental ability or his/her capacity to reason, plan, solve problems, comprehend complex ideas, and learn (AAIDD, 2010). The assessment of intellectual functioning is typically achieved through administration of intelligence quotient (IQ) test. Most IQ tests are structured in the way that a score of 100 is considered average, with a standard deviation of 15 (Hourcade, 2002). In accord to American Association on Intellectual and Developmental Disabilities (AAIDD) guideline, an intellectual level that is considered to be within the range of intellectual disability if it is two or more standard deviations (SDs) below the mean (AAIDD, 2002). In other word, a level of 70 IQ points or lower will be the cut-off point for ID when using an IQ test with a mean of 100 and a standard deviation (SD) of 15, which account for the lowest scoring 2% of the normal population (Flynn, 2000).
Adaptive behavior refers to the collections of conceptual, social, and practical skills that people learn and perform in their everyday lives (AAIDD, 2002). Similar to the assessment of intellectual functioning, adaptive behavior are assessed with instruments which requires observing the individual in situations where these skills are required, or interviewing those who know the individual well (Hourcade, 2002). In AAIDD website, significant limitations in adaptive behavior are operationally defined as performance that is at least two standard deviations below the mean of either (a) one of the following three types of adaptive behavior: conceptual, social, or practical, or (b) an overall score on a standardized measure of conceptual, social, and practical skills.
In general, individuals with ID possess some common characteristics. Typically, individuals with ID will learn and develop more slowly than a typical person because of their cognitive limitations. More often, they present with specific it cognitive deficits such as impairment in memory, attention, or comprehension of language, which often result in their less efficient learning abilities (Hourcade, 2002; Van der Molen, Van Luit, Jongmans, & Van der Molen, 2007). To certain extend, their slower processing, restricted memory or attention can also link to their deficiency in self control and regulation, resulting in impressions that they are more passive or disengaged from activity (Linn, Goodman, & Lender, 2000) or and more distractible or impulsive than others (Goodman & Linn, 2003). Therefore, individuals with ID often require different forms and degree of support in the process of learning and development.
Identification/Diagnosis of ID
The criteria used for identification and diagnosis of ID have evolved from a long way. Schalock and Luckasson (2004) summarize four approaches that have been used to identify persons with ID historically. In the early day, ID was initially identifies not basing on strict criteria, but on individuals' inability to adapt to their social environments. The rise of medical model however has changed the approach of identifying ID. In term, the base of identification was shifted to the person's symptoms complex and clinical syndromes, with the focus on the roles of physical causes and heredity. Later, with the rise of psychometric tests, the criterion for identification and diagnosis of ID was again shifted to individual's intellectual functioning. In term, measures obtained from IQ tests are used as ways to define and classify individuals with ID and their severity of ID. The final shift in the criterion was to an approach they named as 'dual-criterion', where both cognitive functioning and adaptive behaviors were included as criteria of defining ID.
The dual-criterion approach was firstly introduced by AAIDD (was then named as AAMR American Association on Mental Retardation) in 1956 and has been adopted by other diagnostic systems such as the International Classification of Functioning, Disability, and Health (ICF; World Health Organization (WHO), 2001), the Diagnostic and Statistical Manual of Mental Disorders 4th ed., text rev (DSM-IV-TR; American Psychiatric Association, 2000), and the other clinical guidelines used for prevalent definitions of intellectual disabilities such as the International Classification of Diseases, and Related Health Problems 10th revision (ICD-10; WHO, 1992) (Schalock & Luckasson, 2004). The current dual-criterion approach of the classification system also present a paradigm shift in the research and education practice, where intellectual disability is no longer be viewed as person-centered deficit, i.e., characteristic of the individuals. Rather, intellectual disability is contextually determined and with appropriate supports, life functioning of individuals with intellectual disability may improve (Schalock & Luckasson, 2004). With that, the current AAIDD classification system emphasizes the importance of contextual support and intervention to addressing limitations in the areas of intellectual and adaptive functioning.
The AAIDD classification system is one of the most widely used diagnostic systems in the field of research and education identification (Schalock & Luckasson, 2004). The working definition of ID proposed by AAIDD composes of three key components which are also commonly acknowledged by DSM IV-TR and ICF; 1) an IQ score of less than 70; 2) an significant deficit in adaptive function and 3) the onset of disability prior to 18 years of age. Within this system, the three required measures for a diagnosis of ID include an IQ tests, adaptive behavior scales, and documented age of onset.
Identification of ID in clinical settings
The term identification here refers to the process of assessment and diagnosis which a formal diagnosis of ID can be arrived if criteria are met. As mentioned above, internationally, clinical definitions of ID are usually based on established psychiatric diagnostic systems such as ICD-10, ICF and DSM-IV-TR. As noted by Salvador-Carulla and Bertelli (2008), there is little variability in the criteria of the different psychiatric diagnostic systems. Besides addressing on the age onset of the disability, all these systems share a common approach, ie, the assessment of the person should be taken as a whole within the context of the person's intellectual capacities and adaptive functioning in his environment. Nevertheless, minor differences are still present within some criterion among the different diagnostic systems (Salvador-Carulla &Bertelli, 2008). For instance, the cut-off point of the IQ level (AAMR: 70-75; DSM-IV-TR: 70; ICD-10: 69) that classify individuals as having borderline intellectual disability varies among the three major diagnostic systems. Furthermore, the definition of adaptive skills differs among these systems (Colmar, Maxwell & Miller, 2006).
Identification of ID in educational settings
The identification of students with intellectual disability within educational setting evolves parallelly with the changes in the clinical diagnostic systems of this disability (Smith, 1997). Internationally, this revised definition of ID by AAIDD has influenced the development of new classification system in educational setting. In term, the classification of ID has moved from a simplistic IQ-based classification system to a more holistic approach, where a three-step approach is commonly accepted as the standard of classification ID and formulating support. Ee, Tan and Lim (2004) summarize the steps as follow; 1) a formal assessment of IQ and adaptive function; 2) an analysis of individuals in the four dimensions of intellectual functioning and adaptive skills, psychosocial and emotional consideration, physical health and etiology, and environmental consideration; 3) describe the profile and intensities of support needed based on the profile.
Although the above mentioned system has been acknowledged as a new theme for identification of ID in education system, there are still variations in the emphasis and process of identifying ID in educational settings among countries. Colmer, Maxwell and Miller (2006) comment that phenomena such as over-emphasis on IQ score and focusing on disability are still prevalent in educational settings where cognitive ability is often perceived as the base of individual's attainment. In Singapore, the guideline for identification of ID is largely consistent with the diagnostic system of World Health Organization (WHO) (NCSS, 2003), where a formal assessment of adaptive functioning and IQ are necessary when determining the level of limitation and support needed, with a predominant tendency to adhere to the traditional classification system, where the level of disability is associated with IQ scores (Ee, Tan & Lim, 2004).
Educational Placement of students with ID
The placement of students with ID can be classified into three main settings; namely mainstream school, special schools and outside of the education system, i.e., drop-outs (Snell, Luckasson, Borthwick-Duffy &et al, 2009). Snell, Luckasson, Borthwick-Duffy and et al, (2009) describe the national trends of placement for students with ID in the USA. Although inclusion practice has been advocated in the last decade of 20th century in the USA, there are still about 50% of students who are diagnosed with ID receive their educations in separate setting such as special schools. In addition, a significant proportion of students with ID leave school earlier. Cited in Snell, Luckasson, Borthwick-Duffy and et al, (2009), Polloway et al. (2009) reported that in the USA, 28.6% of students with intellectual disabilities drop out form schools during the 2002-2003 school year. Overall, the percentage of students with ID who are fully included in mainstream schools is still relatively low, accounted about 11% in the USA (Snell, Luckasson, Borthwick-Duffy &et al, 2009).
In Singapore, children with ID are placed in both special and mainstream schools, depending on their abilities and needs. Typically, Children with profound disabilities and require extensive support are enrolled in special schools, and children with milder disabilities can be found in all levels of educational systems (Lim & Nam, 2000).
The process of assessment and identification of ID in educational setting is often motivated and guided by a primary goal of enabling a sound educational placement. Traditionally, children with intellectual disabilities are usually enrolled in special education schools (MacMillan & Forness, 1998). With the rise of inclusion movement, the educational placement of children with ID varies among countries. In Singapore, children with intellectual disabilities, including those at mild level are generally enrolled in special schools, in which most of them continue and complete their educations within the special education system (Ee, Tan & Lim, 2004). Whilst in countries such as the USA, where inclusion practice has started for more than a decade, more students with ID are studying in mainstream schools.
Based on estimated prevalence rates, it is suspected a sizable number of children with ID are enrolled in mainstream school (Ee, Tan & lim, 2004)
Screening of ID
It is recognized that planning and intervention for individualized support for individuals with ID are essential in the current era. In order to plan and evaluate the effective and appropriateness of the support service, valid screening and preliminary identification are necessary to facilitate a formal referral and assessment, thus support and intervention. Nevertheless, in contrast to the considerable agreement among professional educators and clinicians as to which guidelines and procedures to follow in diagnosing intellectual disability, there is no consensus on the formal procedures to screen ID (MacMillan & Forness, 1998). As cited in MacMillan and Forness (1998), in the USA, most of the students with ID are firstly screened and referred by their teachers for formal identification of ID by mental health professionals. Similarly, in Singapore, no formal procedures are available when come into the screening of ID. The informal screenings of students with possible intellectual disabilities are usually done by school teachers. In fact, the process of referral for a formal assessment and diagnosis often starts with teacher's observation on students' clear and consistent underachievement in their academic work (Ee, Tan & Lim, 2004).
In other word, due to lacking of formal guidelines for screening process, teachers' knowledge and judgment on the students' abilities play crucial roles in the referral and identification process. Teachers played a key role in the identification of students with special educational needs and in defining the level of support (LOS) they required for each student (McKinnon &Cordon, 1998)
The reasons are described as follow; firstly, since teachers usually refer students after they realize that students' performances are significantly below the norm. The 'norm', i.e., average performance of the student's immediate peers becomes the benchmark for teachers to make decisions for referral. In term, a underachieving students will be more likely referred for formal assessment if he is in a class or school with high-achieving peers, and otherwise less likely to be referred if all his classmates are low-achieving. Secondly, the teachers' relevant knowledge on ID and special needs is also crucial in the process of screening without a formal screening tool (MacMillan & Forness, 1998). In such case, who get referred varies from classroom to classroom as some teachers may have higher tolerance working with academic-weak students, and others may have little capability in dealing with those with difficulty to keep up with school curriculum.
The 'teachers factors' in the process of screening for ID and special needs are even evidenced in X school, where most of students are academic under-achievers, with co morbid behavioral and emotional difficulties. A decision for referral is often less clear-cut when there are multiple problems are calling for attention. Therefore, a standardized screening tool may provide a common metric for teachers to base on when identifying students needing formal assessment and special needs. In line with current diagnostic system, a screening tool with focus on both cognitive ability and adaptive behaviors is necessary when come to a decision for support and placement.
The term inclusion here refers to a practice that students with disabilities are integrated into general education classrooms (Quah, 2004). In inclusive education, individuals with disabilities study full-time in general education classrooms. However, necessary supports may be given during their process of study in general education classrooms (Quah, 2004). Since the late 20th century, inclusive education has become an international trend and agenda (Ainscow, Booth & Dyson, 2006). Policies and legislation have been passed in many parts of the world to promote inclusion in education (Booth, 1999; Bricker, 2000; Harris & Stephenson, 2003; Ainscow, Booth & Dyson, 2006). In response to the shift in legislation in special education, (evidence ofmore inclusion of ID in other countries) Inclusion of Down's syndrome in mainstream school is widely accepted in England after more than 20 years of inclusion campaign (Booth, 1996).
Snell, et al (2009) more ID students are included in regular schools
However, not in Singapore, As pointed out by Lim and Nam (2000), in Singapore, a dual education system catering to students with and without disabilities is still operating. ( Due to lack of training for teachers) Movement towards integrating students with disabilities, especially those with moderate to severe level of disabilities into regular schools remains slow. Teachers still refer their students with ID to special schools
Integrated education is an earlier version and refers to giving extra support to students with special needs who are participating in the mainstream curriculum without major restructuring of content or delivery (Booth, 1996).
. However, the trend of inclusion has also been accepted by society and school personnel. Programs and services have been put forward to facilitate the inclusion of students with physical disabilities and autism (Lim & Nam, 2000). (Add more from LIM and NAM)
Although inclusive education is accepted as an international trend for individuals with disabilities, studies have revealed mixed results of benefits and problems. According to Wong (2002), research studies on inclusive education generally suggest an improvement in social skills and community integration after placement in mainstream school. Whilst, there are also concerns that inclusion was detrimental to meeting the needs of some students if the adaption of curriculum is not tally with their cognitive abilities. In his study on parents' perception on inclusion practice in Hong Kong, Wong (2002) reports that students with disabilities face tremendous difficulty in meeting academic demands in school, which impose obstacles for their effective learning. (? Benefit related to Severity of ID or level of support needed)
Multi-cultural issues in screening and identification
There is always concern that cultural minorities are falsely identified as being intellectual disable. In order to address this concern, MacMillon et al, (1996, as cited in MacMillon and Forness, (1998)) investigate the presence of systemic differences among referred Caucasian, Hispanic and African American students in California. Their findings suggested that the Verbal and Performance IQ of Caucasian students are higher than African American students, leading to a plausible conclusion that schools are unwilling to err in referring minority students.
History of education for children with ID in Singapore
Lack of training on special education among teachers