Intellectual impairment may be either generalised (cognitive impairment) or specific to one area (learning difficulty). Children with cognitive impairment have below-average IQ, at <70.  The degree of cognitive impairment depends on the underlying disorder and its severity. An IQ of 50 to 70 is classed as mild cognitive impairment. Children with a specific learning difficulty, on the other hand, have difficulties with particular mental tasks but a normal IQ. Examples include difficulties with speech (specific language impairment), reading and writing (dyslexia), and use of numbers (dyscalculia). Although the terms 'learning difficulty' and 'cognitive impairment' have specific definitions, they are sometimes used interchangeably by clinicians. 
About 1% of children have cognitive impairment. Down's syndrome and fetal alcohol syndrome are among the most common identified causes of cognitive impairment.  The prevalence of learning difficulties is more difficult to determine because of variation in diagnostic criteria. Most estimates suggest that the lifetime prevalence of learning disability is about 10%; males are more likely to be affected than females. Dyslexia is the most common specific learning disability (affecting about 5% to 12% of children).  
The majority of conditions associated with both specific learning difficulties and generalised cognitive impairment are developmental in origin, are linked to abnormalities in brain structure and function, and are present from birth. Learning difficulty or cognitive impairment may be part of a syndrome, and there may be a family history of similar difficulties. Generalised cognitive impairment is often associated with a history of delayed developmental milestones; the age at which it becomes manifest varies according to its severity. In some children, mild generalised cognitive impairment becomes more obvious when the child starts attending school.
Children who develop new specific learning difficulties or who have recently been identified as having cognitive impairment should be referred to a paediatrician. An acquired disability due to intracranial pathology must be considered if there is an acute onset or a regression of previously acquired skills. However, often the specific learning difficulties or cognitive impairment may have been present for some time but only recently noted (e.g., on starting school).
A multidisciplinary team (MDT) assessment is desirable for accurate diagnosis and advice regarding appropriate interventions and educational placement. An MDT assessment includes the paediatrician or child psychiatrist and allied professionals such as a psychologist and a speech therapist. Children with motor co-ordination difficulties (developmental co-ordination disorder, or dyspraxia) resulting in physical problems with writing may benefit from assessment by an occupational therapist. The role of the clinical psychologist is to identify the child's cognitive ability (IQ, or age-equivalent developmental level, which can be compared with their chronological age). Speech therapists help assess the child's expressive and receptive (understanding) language abilities and compare these with the overall level of cognitive ability. Some children have a discrepancy between cognitive and language abilities. For example, children with autism sometimes have relatively superior non-verbal skills compared with verbal performance.
The name 'cerebral palsy' is a diagnostic term given to children with a static brain injury of varying aetiology (e.g., premature birth, hypoxic-ischaemic injury, meningitis, or intracerebral haemorrhage), associated with a disorder of movement and posture. Cerebral palsy is not a cause of cognitive impairment. However, the two conditions can co-exist, and for this reason a cause-and-effect relationship is often mistakenly assumed both by clinicians and by the general public. 
Director of Pediatric Neurology
Cortica | Advanced Neurological Therapies for Autism
KAS declares that he has no competing interests.
Dr Kevin A. Shapiro would like to gratefully acknowledge Dr Jeremy Parr, the previous contributor to this monograph. JP is an author of a number of references cited in this monograph.
Consultant in Paediatric Neurodisability
Evelina Children's Hospital
St Thomas' Hospital
PG declares that he has no competing interests.
Assistant Professor of Pediatrics
Department of Pediatrics
University of Rochester Medical Center
SHJ declares that she has no competing interests.
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