Specific Language Impairment and Developmental Language Disorder

Developmental language disorder (DLD), historically termed specific language impairment (SLI), is a neurodevelopmental condition in which language fails to develop as expected, in the absence of a known biomedical cause such as hearing loss, intellectual disability, or a recognised syndrome. Children with DLD have persistent difficulties understanding or using spoken language that interfere with everyday communication and learning.

Definition

Developmental language disorder is a persistent impairment in the acquisition and use of language - affecting vocabulary, grammar, and discourse in comprehension, production, or both - that emerges in early development, is not attributable to another condition that would better explain it, and has a functional impact on communication or learning.

Scope

This entry covers the definition and terminology of DLD and SLI, the language domains typically affected, the shift in diagnostic criteria away from nonverbal-IQ discrepancy, prevalence in the population, and the relationship to later literacy and educational outcomes. It is a reference description of the condition, not an assessment or intervention protocol.

Core questions

• What distinguishes DLD from typical late language emergence that resolves?
• Why did the field move from specific language impairment to developmental language disorder?
• Which grammatical and lexical markers are characteristic of the disorder?
• How does early DLD relate to later reading and academic difficulties?

Key concepts

• Developmental language disorder versus specific language impairment terminology
• Exclusionary versus functional-impact diagnostic criteria
• Tense and grammatical morphology as clinical markers
• Nonverbal IQ discrepancy debate
• Heritability and family aggregation
• Continuity with literacy disorders

Mechanisms

DLD reflects atypical development of the brain's language network with a strong genetic contribution, evidenced by high heritability and familial aggregation rather than a single causal lesion. Affected children often show characteristic weaknesses in grammatical morphology - for example, marking of verb tense and agreement - and in processing and retaining verbal material, though profiles vary. Because the impairment is developmental, it tends to persist and to shape downstream skills such as reading comprehension rather than resolving spontaneously.

Clinical relevance

DLD is one of the most common neurodevelopmental conditions and frequently co-occurs with reading difficulty, attention problems, and social challenges, so its recognition matters across speech-language pathology and education. This entry describes the disorder as a clinical entity; identification and management of an individual child require professional evaluation and are outside the scope of this reference.

Epidemiology

Epidemiological studies place the prevalence of unexplained language disorder at roughly 7 percent of children at school entry in the population study of Norbury and colleagues, broadly consistent with earlier kindergarten estimates from Tomblin and colleagues. Boys are somewhat more often identified than girls, and the condition is frequently under-recognised relative to its prevalence.

History

The condition was described under labels including congenital aphasia and developmental dysphasia before specific language impairment became dominant in the late twentieth century, anchored by exclusionary criteria and nonverbal-IQ discrepancy. Tomblin's 1997 prevalence study and Leonard's synthesis defined the SLI era. The CATALISE Delphi consensus led by Bishop (2016, 2017) then established developmental language disorder as the preferred term, removing the requirement for a nonverbal-IQ discrepancy and emphasising functional impact.

Debates

Should a nonverbal-IQ discrepancy define the disorder?

The SLI tradition required language to be impaired relative to nonverbal ability; the CATALISE consensus rejected strict IQ cut-offs after evidence that children above and below such thresholds have similar profiles and respond similarly, favouring functional impact instead.

Is grammatical morphology the core deficit?

Tense and agreement marking are robust clinical markers in English-speaking children, but whether grammar is the central impairment or one facet of a broader processing limitation remains debated and varies across languages.

Key figures

• Dorothy Bishop
• Laurence Leonard
• Courtenay Norbury
• J. Bruce Tomblin
• Margaret Snowling

Seminal works

• bishop-2016-catalise1
• bishop-2017-catalise2
• norbury-2016
• tomblin-1997

Frequently asked questions

Is developmental language disorder the same as specific language impairment?

They refer to largely the same children. Developmental language disorder is the term endorsed by the CATALISE consensus and is now preferred; specific language impairment is the older label that required a discrepancy with nonverbal IQ.

Does a child with DLD have low intelligence?

Not necessarily. DLD is defined by language difficulty that is not explained by another condition; many children with DLD have nonverbal abilities in the typical range, which is why the field moved away from IQ-discrepancy criteria.