Specific language impairment
Specific language impairment (SLI) is diagnosed when a child's language does not develop normally and the difficulties cannot be accounted for by generally slow development, physical abnormality of the speech apparatus, autistic disorder, acquired brain damage or hearing loss.
- 1 Classification
- 2 Diagnosis
- 3 Prevalence
- 4 Developmental course and outcome
- 5 Genetic and environmental risks
- 6 Causal theories
- 7 Associated factors
- 8 Intervention
- 9 See also
- 10 References
- 11 Further reading
- 12 External links
Specific language impairment (SLI) is diagnosed when a child has delayed or disordered language development for no apparent reason. Usually the first indication of SLI is that the child is later than usual in starting to speak and subsequently is delayed in putting words together to form sentences. Spoken language may be immature. In many children with SLI, understanding of language, or receptive language, is also impaired, though this may not be obvious unless the child is given a formal assessment. Although difficulties with use and understanding of complex sentences are a common feature of SLI, the diagnostic criteria encompass a wide range of problems, and for some children other aspects of language are problematic (see below). In general, the term SLI is reserved for children whose language difficulties persist into school age, and so it would not be applied to toddlers who are late to start talking, most of whom catch up with their peer group after a late start.
The terminology for children’s language disorders is extremely wide-ranging and confusing, with many labels that have overlapping but not necessarily identical meanings. In part this confusion reflects uncertainty about the boundaries of SLI, and the existence of different subtypes. Historically, the terms ‘’developmental dysphasia’’ or ‘’developmental aphasia’’ were used to describe children with the clinical picture of SLI. These terms have, however, largely been abandoned, as they suggest parallels with adult acquired aphasia. This is misleading, as SLI is not caused by brain damage. In medical circles, terms such as specific developmental language disorder are often used, but this has the disadvantage of being wordy, and is also rejected by some people who think SLI should not be seen as a ‘disorder’. In the UK educational system, speech, language and communication needs (SLCN) is currently the term of choice, but this is far broader than SLI, and includes children with speech and language difficulties arising from a wide range of causes.
Subtypes (Rapin and Allen 1987)
Although most experts agree that children with SLI are quite variable, there is little agreement on how best to subtype them. There is no widely accepted classification system. In 1983 Rapin and Allen  proposed a classification of developmental language disorders based on the linguistic features of language impairment, which was subsequently updated by Rapin. Note that Rapin is a child neurologist, and she refers to different subtypes as ‘syndromes’; many of those coming from the perspective of education or speech-language therapy reject this kind of medical label, and argue that there is not a clear dividing line between SLI and normal variation. Also, although most experts would agree that children with characteristics of the Rapin subtypes can be identified, there are many cases who are less easy to categorise, and there is also evidence that categorisation can change over time.
Rapin's subgroups fall into three broad categories:
Receptive/expressive developmental language disorder
Receptive/expressive phonologic/syntactic deficit syndrome. This is the most common form of SLI, in which the child’s most obvious problems are a tendency to speak in short, simplified sentences, with omission of some grammatical features, such as past tense -ed. It is common also to see simplified speech production when the child is young. For instance, clusters of consonants may be reduced, so that ‘string’ is pronounced as ‘ting’. Vocabulary is often limited, with a tendency to use ‘general all-purpose’ terms, rather than more specific words.
Verbal auditory agnosia. This is a very rare form of language impairment, in which the child appears unable to make sense of speech sounds. It typically occurs as a symptom of Landau-Kleffner syndrome, in which case a diagnosis of SLI would not be appropriate, as there is a known neurological origin of the language difficulties.
Expressive developmental language disorder syndromes
Developmental verbal dyspraxia (DVD). In the child with DVD, comprehension is adequate; the onset of speech is very delayed and extremely limited with impaired production of speech sounds and short utterances. The poor speech production cannot be explained in terms of structural or neurological damage of the articulators. There is much disagreement about diagnostic criteria, but the label most often used for children whose intelligibility declines markedly when they attempt complex utterances, compared to when they are producing individual sounds or syllables. Another key feature is inconsistency of speech sound production from one occasion to another. Although the term 'dyspraxia' suggests a pure output disorder, many – perhaps all- of these children have difficulty in doing tasks that involve mentally manipulating speech sounds, such as phonological awareness tasks. Children with DVD also typically have major literacy problems, and receptive language levels may be poor on tests of vocabulary and grammar
Phonologic programming deficit syndrome. The child speaks in long but poorly intelligible utterances, producing what sounds like jargon. Outside Rapin’s group, little has been written about this subtype, which is not generally recognised in diagnostic frameworks.
Higher order processing disorders
Lexical deficit disorder. The child has word finding problems and difficulty putting ideas into words. There is poor comprehension for connected speech. Again, there is little research on this subtype, which is not widely recognised.
Pragmatic language impairment. The child speaks in fluent and well-formed utterances with adequate articulation; content of language is unusual; comprehension may be over-literal; language use is odd; the child may chatter incessantly, be poor at turn-taking in conversation and maintaining a topic. There has been a great deal of controversy about this category, which is termed pragmatic language impairment (PLI) in the UK. Debate has centred over the question of whether it is a subtype of SLI, part of the autistic spectrum, or a separate condition. In DSM5, the term Social Communication Disorder has been introduced; this is equivalent to PLI.
Relationship with other neurodevelopmental disorders
Although textbooks draw clear boundaries between different neurodevelopmental disorders, there is much debate about overlaps between them. Many children with SLI meet diagnostic criteria for developmental dyslexia, and others have features of autism.
SLI is defined purely in behavioural terms: there is no biological test for SLI. There are three points that need to be met for a diagnosis of SLI:
- The child has language difficulties that interfere with daily life or academic progress
- Other causes are excluded: the problems cannot be explained in terms of hearing loss, general developmental delay, autism, or physical difficulty in speaking
- Performance on a standardized language test (see Assessment, below) is significantly below age level
There is considerable variation in how this last criterion is implemented. Tombin et al. (1996) proposed the EpiSLI criterion, based on five composite scores representing performance in three domains of language (vocabulary, grammar, and narration) and two modalities (comprehension and production). Children scoring in the lowest 10% on two or more composite scores are identified as having language disorder.
Assessment will usually include an interview with the child’s caregiver, observation of the child in an unstructured setting, a hearing test, and standardized tests of language and nonverbal ability. There is a wide range of language assessments in English. Some are restricted for use by speech and language professionals (therapists or SALTs in the UK, speech-language pathologists, SLPs, in the US and Australia). A commonly used test battery for diagnosis of SLI is the Clinical Evaluation of Language Fundamentals (CELF). Assessments that can be completed by a parent or teacher can be useful to identify children who may require more in-depth evaluation. The Grammar and Phonology Screening (GAPS) test is a quick (ten minute) simple and accurate screening test developed and standardized in the UK. It is suitable for children from 3;4 to 6;8 years;months and can be administered by professionals and non-professionals (including parents) alike, and has been demonstrated to be highly accurate (98% accuracy) in identifying impaired children who need specialist help vs non-impaired children. This makes it potentially a feasible test for widespread screening. 'The Children’s Communication Checklist CCC–2' is a parent questionnaire suitable for testing language skills in school-aged children.
Epidemiological surveys, in the US and Canada, estimated the prevalence of SLI in 5-year-olds at around 7 per cent. However, neither study adopted the stringent 'discrepancy' criteria of the Diagnostic and Statistical Manual of Mental Disorders or ICD-10; SLI was diagnosed if the child scored below cut-off on standardized language tests, but had a nonverbal IQ of 90 or above and no other exclusionary criteria.
Developmental course and outcome
Longitudinal studies indicate that problems are largely resolved by 5 years in around 40% of 4-year-olds with SLI. However, for children who still have significant language difficulties at school entry low levels of literacy are common, even for children who receive specialist help, and educational attainments are typically poor. Poor outcomes are most common in cases where comprehension as well as expressive language is affected.
SLI is associated with a high rate of psychiatric disorder. For instance, Conti-Ramsden and Botting (2004) found that 64% of a sample of 11-year-olds with SLI scored above a clinical threshold on a questionnaire for psychiatric difficulties, and 36% were regularly bullied, compared with 12% of comparison children. In the longer-term, studies of adult outcomes of children with SLI find elevated rates of unemployment, social isolation and psychiatric disorder. However, most studies focused on children with severe problems, where comprehension as well as expressive language was affected. Better outcomes are found for children who have milder difficulties and do not require special educational provision.
Genetic and environmental risks
It is now generally accepted that SLI is a strongly genetic disorder. The best evidence comes from studies of twins. Two twins growing up together are exposed to the same home environment, yet may differ radically in their language skills. Such different outcomes are, however, seen almost exclusively in fraternal (non-identical) twins, who are genetically different. Identical twins share the same genes and tend to be much more similar in language ability. There can be some variation in the severity and persistence of SLI in identical twins, indicating that environmental factors affect the course of disorder, but it is unusual to find a child with SLI who has an identical twin with normal language. SLI is not usually caused by a mutation in a single gene. Current evidence suggests that there are many different genes that can influence language learning, and SLI results when a child inherits a particularly detrimental combination of risk factors, each of which may have only a small effect. Only a handful of non-genetic factors have been found selectively to impact on language development in children. Later-born children in large families are at greater risk than earlier born.
Much research has focussed on trying to identify what makes language learning so hard for some children. A major divide is between theories that attribute the difficulties to a low-level problem with auditory temporal processing, and those that propose there is a deficit in a specialised language-learning system. Other accounts emphasise deficits in specific aspects of memory. It can be difficult to choose between theories because they do not always make distinctive predictions, and there is considerable heterogeneity among children with SLI. It has also been suggested that SLI may only arise when more than one underlying deficit is present.
Males are more affected by SLI than females. In clinical samples, the sex ratio of affected males: females is around 3 or 4:1. The reason for this association is not known: no linkage has been found to genes on the sex chromosomes. Poor motor skills are commonly found in children with SLI. Brain scans do not usually reveal any obvious abnormalities in children with SLI, although quantitative comparisons have found differences in brain size or relative proportions of white or grey matter in specific regions. In some cases, unusual brain gyri are found. To date, no consistent 'neural signature' for SLI has been found. Differences in the brains of children with SLI vs typically developing children are subtle and may overlap with atypical patterns seen in other neurodevelopmental disorders.
Intervention is usually carried out by speech and language therapists, who use a wide range of techniques to stimulate language learning. In the past, there was a vogue for drilling children in grammatical exercises, using imitation and elicitation methods, but such methods fell into disuse when it became apparent that there was little generalisation to everyday situations. Contemporary approaches to enhancing development of language structure are more likely to adopt 'milieu' methods, in which the intervention is interwoven into natural episodes of communication, and the therapist builds on the child's utterances, rather than dictating what will be talked about. In addition, there has been a move away from a focus solely on grammar and phonology toward interventions that develop children's social use of language, often working in small groups that may include typically developing as well as language-impaired peers. Another way in which modern approaches to remediation differ from the past is that parents are more likely to be directly involved, particularly with preschool children. A radically different approach has been developed by Tallal and colleagues, who have devised a computer-based intervention, Fast Forword, that involves prolonged and intensive training on specific components of language and auditory processing. The theory underlying this approach maintains that language difficulties are caused by a failure to make fine-grained auditory discriminations in the temporal dimension, and the computerised training materials are designed to sharpen perceptual acuity. For all these types of intervention, there are few adequately controlled trials that allow one to assess clinical efficacy. In general, where studies have been done, results have been disappointing, though some more positive outcomes have been reported. In 2010, a systematic review of clinical trials assessing the FastForword approach was published, and reported no significant gains relative to a control group.
- Bishop, D ; Norbury, C. F. (2008). "Speech and language impairments". In Anita Thapar; Sir Michael Rutter; Bishop, Dorothy ; Daniel Pine; Scott, Steven M.; Jim Stevenson; Taylor, Eric; Eds. Rutter's Child and Adolescent Psychiatry. Oxford: Wiley-Blackwell. pp. 782–801. ISBN 1-4051-4549-8. OCLC 473789535.
- Bishop, D. (1997). Uncommon understanding: development and disorders of language comprehension in children. East Sussex: Psychology Press. ISBN 0-86377-260-9. OCLC 776282908.
- Donna J. Thal; Jeanette Katich; (1996). "Predicaments in early identification of specific language impairment : does the early bird always catch the worm?". In Donna J. Thal; Kevin N. Cole; Dale, Philip S. Assessment of Communication and Language (Communication and Language Intervention Series). Brookes Publishing Company. pp. 1–28. ISBN 1-55766-193-6. OCLC 34772171.
- Ingram TT, Reid JF (June 1956). "Developmental aphasia observed in a department of child psychiatry". Arch. Dis. Child. 31 (157): 161–72. PMC 2011959. PMID 13328151.
- Bishop, D. V. M (2004). "Specific language impairment: diagnostic dilemma". In Hans Van Balkom; Verhoeven, Ludo Th. Classification of developmental language disorders: theoretical issues and clinical implications. Hillsdale, N.J: Lawrence Erlbaum. pp. 309–326. ISBN 1-4106-0902-2. OCLC 53721852.
- Rapin, I., & Allen, D. (1983). Developmental language disorders: nosologic considerations. In U. Kirk (Ed.), Neuropsychology of language, reading, and spelling (pp. 155–184). New York: Academic Press.
- Rapin I (September 1996). "Practitioner review: developmental language disorders: a clinical update". J Child Psychol Psychiatry 37 (6): 643–55. doi:10.1111/j.1469-7610.1996.tb01456.x. PMID 8894945.
- Dale, P. S., & Cole, K. N. (1991). What's normal? Specific language impairment in an individual differences perspective. Language, Speech and Hearing Services in Schools, 22, 80–83.
- Conti-Ramsden G, Botting N (October 1999). "Classification of children with specific language impairment: longitudinal considerations". J. Speech Lang. Hear. Res. 42 (5): 1195–204. PMID 10515515.
- Leonard, Laurence B. (1998). Children with specific language impairment. Cambridge, Mass: The MIT Press. ISBN 0-585-27859-8. OCLC 45728290.
- Rice, M. L.; Bode, J. V. (1993). "GAPS in the verb lexicons of children with specific language impairment". First Language 13 (37): 113–131. doi:10.1177/014272379301303707. ISSN 0142-7237.
- Leonard LB (May 2009). "Is expressive language disorder an accurate diagnostic category?". Am J Speech Lang Pathol 18 (2): 115–23. doi:10.1044/1058-0360(2008/08-0064). PMC 2718760. PMID 19029534.
- Hill EL (2001). "Non-specific nature of specific language impairment: a review of the literature with regard to concomitant motor impairments". Int J Lang Commun Disord 36 (2): 149–71. PMID 11344592.
- Wells, Bill; Stackhouse, Joy (1997). Children's speech and literacy difficulties: a psycholinguistic framework. San Diego, Calif: Singular Pub. Group. ISBN 1-86156-030-3. OCLC 246491090.
- Bishop, D. V. M. (2000). Pragmatic language impairment: a correlate of SLI, a distinct subgroup, or part of the autistic continuum? In D. V. M. Bishop & L. B. Leonard (Eds.), Speech and Language Impairments in Children: Causes, Characteristics, Intervention and Outcome (pp. 99–113). Hove, UK: Psychology Press.
- Bishop, D., & Rutter, M. (2008). Neurodevelopmental disorders: conceptual approaches. In M. Rutter, D. Bishop, D. Pine, S. Scott, J. Stevenson, E. Taylor & A. Thapar (Eds.), Rutter's Child and Adolescent Psychiatry (pp. 32–41). Oxford: Blackwell.
- Bishop DV, Snowling MJ (November 2004). "Developmental dyslexia and specific language impairment: same or different?". Psychol Bull 130 (6): 858–86. doi:10.1037/0033-2909.130.6.858. PMID 15535741.
- Bishop, D. V. M. (2008). Specific language impairment, dyslexia, and autism: Using genetics to unravel their relationship. In C. F. Norbury, J. B. Tomblin & D. V. M. Bishop (Eds.), Understanding developmental language disorders: from theory to practice (pp. 67–78). Hove: Psychology Press.
- Tomblin JB, Records NL, Zhang X (December 1996). "A system for the diagnosis of specific language impairment in kindergarten children". J Speech Hear Res 39 (6): 1284–94. PMID 8959613.
- Gardner H, Froud K, McClelland A, van der Lely HK (2006). "Development of the Grammar and Phonology Screening (GAPS) test to assess key markers of specific language and literacy difficulties in young children". Int J Lang Commun Disord 41 (5): 513–40. doi:10.1080/13682820500442644. PMID 17050469.
- van der Lely HK, Payne E, McClelland A (2011). "An investigation to validate the grammar and phonology screening (GAPS) test to identify children with specific language impairment". PLoS ONE 6 (7): e22432. doi:10.1371/journal.pone.0022432. PMC 3145645. PMID 21829461.
- Tomblin JB, Records NL, Buckwalter P, Zhang X, Smith E, O'Brien M (December 1997). "Prevalence of specific language impairment in kindergarten children". J. Speech Lang. Hear. Res. 40 (6): 1245–60. PMID 9430746.
- Johnson CJ, Beitchman JH, Young A, et al. (June 1999). "Fourteen-year follow-up of children with and without speech/language impairments: speech/language stability and outcomes". J. Speech Lang. Hear. Res. 42 (3): 744–60. PMID 10391637.
- Bishop DV, Edmundson A (May 1987). "Language-impaired 4-year-olds: distinguishing transient from persistent impairment". J Speech Hear Disord 52 (2): 156–73. PMID 3573746.
- Catts HW, Fey ME, Tomblin JB, Zhang X (December 2002). "A longitudinal investigation of reading outcomes in children with language impairments". J. Speech Lang. Hear. Res. 45 (6): 1142–57. doi:10.1044/1092-4388(2002/093). PMID 12546484.
- Snowling MJ, Adams JW, Bishop DV, Stothard SE (2001). "Educational attainments of school leavers with a preschool history of speech-language impairments". Int J Lang Commun Disord 36 (2): 173–83. PMID 11344593.
- Simkin, Z.; Conti-Ramsden, G. (2006). "Evidence of reading difficulty in subgroups of children with specific language impairment". Child Language Teaching and Therapy 22 (3): 315–331. doi:10.1191/0265659006ct310xx. ISSN 0265-6590.
- Cohen, Nancy (2001). Language impairment and psychopathology in infants, children, and adolescents. Thousand Oaks: Sage Publications. ISBN 0-7619-2025-0. OCLC 45749780.
- Conti-Ramsden G, Botting N (February 2004). "Social difficulties and victimization in children with SLI at 11 years of age". J. Speech Lang. Hear. Res. 47 (1): 145–61. doi:10.1044/1092-4388(2004/013). PMID 15072535.
- Clegg J, Hollis C, Mawhood L, Rutter M (February 2005). "Developmental language disorders—a follow-up in later adult life. Cognitive, language and psychosocial outcomes". J Child Psychol Psychiatry 46 (2): 128–49. doi:10.1111/j.1469-7610.2004.00342.x. PMID 15679523.
- Snowling MJ, Bishop DV, Stothard SE, Chipchase B, Kaplan C (August 2006). "Psychosocial outcomes at 15 years of children with a preschool history of speech-language impairment". J Child Psychol Psychiatry 47 (8): 759–65. doi:10.1111/j.1469-7610.2006.01631.x. PMID 16898989.
- Bishop DV (October 2006). "What Causes Specific Language Impairment in Children?". Curr Dir Psychol Sci 15 (5): 217–221. doi:10.1111/j.1467-8721.2006.00439.x. PMC 2582396. PMID 19009045.
- Bishop, D. V. M. (2009). Genes, cognition and communication: insights from neurodevelopmental disorders. The Year in Cognitive Neuroscience: Annals of the New York Academy of Sciences, 1156, 1–18.
- Garside, Roger F.; Fundudis, Trian; Kolvin, Israel (1979). Speech retarded and deaf children : their psychological development. Boston: Academic Press. ISBN 0-12-270150-X. OCLC 6308388.
- Ceponiene R, Cummings A, Wulfeck B, Ballantyne A, Townsend J (September 2009). "Spectral vs. temporal auditory processing in specific language impairment: a developmental ERP study". Brain Lang 110 (3): 107–20. doi:10.1016/j.bandl.2009.04.003. PMC 2731814. PMID 19457549.
- Tallal P (September 2004). "Improving language and literacy is a matter of time". Nat. Rev. Neurosci. 5 (9): 721–8. doi:10.1038/nrn1499. PMID 15322530.
- Rice ML, Wexler K, Cleave PL (August 1995). "Specific language impairment as a period of extended optional infinitive". J Speech Hear Res 38 (4): 850–63. PMID 7474978.
- van der Lely HK (February 2005). "Domain-specific cognitive systems: insight from Grammatical-SLI". Trends Cogn. Sci. (Regul. Ed.) 9 (2): 53–9. doi:10.1016/j.tics.2004.12.002. PMID 15668097.
- Lum JA, Gelgic C, Conti-Ramsden G (2010). "Procedural and declarative memory in children with and without specific language impairment". Int J Lang Commun Disord 45 (1): 96–107. doi:10.3109/13682820902752285. PMC 2826154. PMID 19900077.
- Ullman MT, Pierpont EI (June 2005). "Specific language impairment is not specific to language: the procedural deficit hypothesis". Cortex 41 (3): 399–433. PMID 15871604.
- Montgomery JW (2003). "Working memory and comprehension in children with specific language impairment: what we know so far". J Commun Disord 36 (3): 221–31. doi:10.1016/S0021-9924(03)00021-2. PMID 12742669.
- Montgomery JW, Magimairaj BM, Finney MC (February 2010). "Working memory and specific language impairment: an update on the relation and perspectives on assessment and treatment". Am J Speech Lang Pathol 19 (1): 78–94. doi:10.1044/1058-0360(2009/09-0028). PMID 19948760.
- Gathercole, Susan E; Baddeley, Alan D (1990). "Phonological memory deficits in language disordered children: Is there a causal connection?". Journal of Memory and Language 29 (3): 336–360. doi:10.1016/0749-596X(90)90004-J. ISSN 0749-596X.
- Coady JA, Evans JL (2008). "Uses and interpretations of non-word repetition tasks in children with and without specific language impairments (SLI)". Int J Lang Commun Disord 43 (1): 1–40. doi:10.1080/13682820601116485. PMID 18176883.
- Hsu HJ, Bishop DV (January 2011). "Grammatical Difficulties in Children with Specific Language Impairment: Is Learning Deficient?". Hum Dev 53 (5): 264–277. doi:10.1159/000321289. PMC 3191529. PMID 22003258.
- Bishop DV (July 2006). "Developmental cognitive genetics: how psychology can inform genetics and vice versa". Q J Exp Psychol (Hove) 59 (7): 1153–68. doi:10.1080/17470210500489372. PMC 2409179. PMID 16769616.
- Robinson, R. J. (1991). Causes and associations of severe and persistent specific speech and language disorders in children. Developmental Medicine and Child Neurology, 33, 943–962.
- Jernigan TL, Hesselink JR, Sowell E, Tallal PA (May 1991). "Cerebral structure on magnetic resonance imaging in language- and learning-impaired children". Arch. Neurol. 48 (5): 539–45. PMID 2021369.
- Jackson T, Plante E (June 1996). "Gyral morphology in the posterior Sylvian region in families affected by developmental language disorder". Neuropsychol Rev 6 (2): 81–94. PMID 8976499.
- Herbert MR, Kenet T (June 2007). "Brain abnormalities in language disorders and in autism". Pediatr. Clin. North Am. 54 (3): 563–83, vii. doi:10.1016/j.pcl.2007.02.007. PMID 17543910.
- Bishop DV (September 2010). "Overlaps between autism and language impairment: phenomimicry or shared etiology?". Behav. Genet. 40 (5): 618–29. doi:10.1007/s10519-010-9381-x. PMC 2921070. PMID 20640915.
- Gallagher, T. (1996). Social-interactional approaches to child language intervention. In J. Beitchman, N. J. Cohen, M. M. Konstantareas & R. Tannock (Eds.), Language, Learning and Behavior Disorders: Developmental, Biological and Clinical Perspectives (pp. 493–514). New York: Cambridge University Press.
- Tannock, R., & Girolametto, L. (1992). Reassessing parent-focused intervention programs. In S. F. Warren & J. Reichle (Eds.), Causes and effects in communication and language intervention (pp. 49–81). Baltimore MD: Paul Brooks.
- Tallal, P. (2000). Experimental studies of language learning impairments: From research to remediation. In D. V. M. Bishop & L. B. Leonard (Eds.), Speech and Language Impairments in Children: Causes, Characteristics, Intervention and Outcome (pp. 131–155). Hove, UK: Psychology Press.
- Law J, Garrett Z, Nye C (August 2004). "The efficacy of treatment for children with developmental speech and language delay/disorder: a meta-analysis". J. Speech Lang. Hear. Res. 47 (4): 924–43. doi:10.1044/1092-4388(2004/069). PMID 15324296.
- Glogowska M, Roulstone S, Enderby P, Peters TJ (October 2000). "Randomised controlled trial of community based speech and language therapy in preschool children". BMJ 321 (7266): 923–6. PMC 27499. PMID 11030677.
- Bryne-Saricks, M. C. (1987). Treatment of language disorders in children: a review of experimental studies. In H. Winitz (Ed.), Human Communication and its Disorders (pp. 167–201). Norwood, N. J: Ablex Publishing.
- Strong, G. K., Torgerson, C. J., Torgerson, D., & Hulme, C. (2010). A systematic meta-analytic review of evidence for the effectiveness of the ‘Fast ForWord’ language intervention program. Journal of Child Psychology and Psychiatry, in press, doi:10.1111/j.1469-7610.2010.02329.x.
- Paul, Rhea (2007). Language disorders from infancy through adolescence: assessment & intervention. Mosby Elsevier. ISBN 0-323-03685-6. OCLC 487807750.