Developmental Language Disorder (DLD) is a problem understanding and/or using language. From an early age, children with DLD will have difficulty using language when they talk or understand other people’s talk. This is despite normal intelligence and opportunity. Most cases of DLD do not have a known cause. Developmental Language Disorder affects speech sounds, learning and memory, social language, discourse, sentences, and words.

What we know about Developmental Language Disorder

  • DLD is a hidden disability.
  • DLD is not caused by a neurological deficit or lack of exposure to language.
  • Children with DLD make more errors or use simpler sentences or even have trouble organising a conversation.
  • DLD emerges in early childhood but persists into adulthood.
  • DLD is common. Approximately 1 in 14 children have DLD. That’s two children in every classroom.
  • DLD is a life-long condition that impairs social and academic functions.

Symptoms of Developmental Language Disorder

Difficulties are often picked up during childhood, although a teenager or adult can be diagnosed with DLD. Children with DLD may:

  • struggle to find the words to express ideas
  • have trouble organising sentences, having conversations, or telling a story
  • find it hard to understand words, follow instructions or answer questions
  • not remember what someone has said
  • have difficulty with behaviour and paying attention
  • have difficulty reading and writing.

How is DLD diagnosed?

DLD is best diagnosed by a Speech Language Therapist (SLT). It is a diagnosis based on behaviours, not brain scans or blood tests. DLD is not usually diagnosed before age 5 years, at a time when the child’s language system is well established. Typically, the SLT will assess the child’s interest in communicating and the ability of the child to understand and express words and sentences. The SLT administers a battery of language tests and compares the child’s performance to that of other children the same age from a normative sample. The functional impact of any language difficulty should also be assessed through observations of social interactions, considerations of academic achievement, and interviewing the individual or the family. A combination of low performance on the tests and evidence that the low language abilities are causing problems in everyday life can lead to a diagnosis of DLD.

Treatment of Developmental Language Disorder

Early diagnosis of DLD is important and can help to improve long-term outcomes. Children with DLD will benefit from individualised intervention delivered by a SLT. With the right support and intervention, children with DLD can improve skills like vocabulary, narrative discourse, comprehension, and phonological awareness. The child’s speech therapist will also support parents and teachers. They will suggest ideas and strategies that will help the child with DLD at home and in the classroom to reduce the impact of their communication difficulties.

The Relationship Between Developmental Language Disorder and Dyslexia

Although DLD affects spoken language, children and adults with DLD often have difficulty with written language – reading, spelling, and writing as well. A good foundation of spoken language supports children as they learn to read and write, so naturally, children with DLD are at risk for written language problem.

There is an important overlap of concepts when it comes to reading. Being a good reader means more than only reading the words on the page – you need to understand what you are reading, too. Reading comprehension is the product of accurate and efficient word reading and language comprehension. When assessing people with reading problems, we need to look at both decoding skills (which may be relevant to a diagnosis of reading difficulties or dyslexia), as well as general language comprehension skills (which may be relevant to a diagnosis of DLD).

Dyslexia in general terms involves a severe difficulty learning how to read. DLD is an unexpected deficit in expressive and/or receptive language abilities. Both Dyslexia and DLD:

  • are disorders that affect language
  • are deficits that are ‘unexpected’ given the absence of intellectual disabilities or other medical explanations; and
  • developmental language disorder and dyslexia are both neurodevelopmental in nature meaning that they are likely to be heritable, emerge early in development and persist across the life-span
  • developmental language disorder and dyslexia require the child to have received adequate environmental stimulation including appropriate reading instruction for dyslexia, and adequate human language interactions for DLD.

The key point is that good reading comprehension requires good decoding skills and good language comprehension skills. Deficits in either (or both) can cause clinically significant reading problems. In other words, children with dyslexia and many children with DLD have reading problems. But reading problems can be caused by decoding problems, language comprehension problems or both – and it is essential to find out which deficits are contributing to a child’s difficulty reading so that you can plan the right intervention.


Difference #1. Phonological deficits vs. multi-dimensional language deficits

In dyslexia, the principal deficit is word reading. Most definitions of dyslexia include marked difficulties with word reading, decoding, and spelling. Many descriptions focus on phonological deficits as a core feature of dyslexia. Phonology is the system of contrastive relationships among the speech sounds that constitute the fundamental components of a language. Phonological deficits impact the specificity at which sounds are stored and recalled in words, as well as the reader’s ability to manipulate sounds in words and connect sounds to letters to read words.

In DLD, children may have language deficits across multiple dimensions of language. These can include phonology. But they can also affect vocabulary, semantic knowledge, morphology, syntax and the social use of language. This is the so-called content, form, and use of language.

Difference #2. Biologically primary v. secondary knowledge

Oral language is biologically primary knowledge – humans as a species have a natural instinct for it. Reading words is biologically secondary – or unnatural. In evolutionary terms, decoding written words is a recent development and everyone must learn how to do it. Incidentally, that’s one reason why many definitions of dyslexia (controversially) exclude reading problems caused by poor instruction. Otherwise, everyone who was illiterate would be dyslexic, which is not the case.

Conclusion: Key Points

DLD and dyslexia are distinct disorders that can co-occur. It is well established that oral language is the foundation of learning to read and that children with a history of oral language difficulties are at high risk of reading problems. The nature of each individual child’s reading problem differs according to their language profile. Phonological deficits are strongly associated with poor decoding while problems with vocabulary, grammar, and receptive language are more strongly associated with reading comprehension difficulties. It is important to recognise that many children have both decoding and reading comprehension problems.

Summary – Key points

  • DLD and dyslexia frequently co-occur, although no one knows exactly how often. It is likely that many children identified with reading difficulties in schools will have co-occurring (but perhaps undiagnosed) DLD.
  • Poor reading comprehension is the result of poor decoding in dyslexia, while it is the result of poor language skills in children with DLD.
  • Evidenced-based interventions can promote reading and language skills in children at high risk of poor literacy and consequent poor educational attainments.
  • Many children with dyslexia who perform within normal limits on standardised language tests may still have significant (if sub-clinical) language difficulties that requiring monitoring and support.
  • Students with dyslexia – regardless of whether they also have DLD – are at risk of slower language acquisition and slower growth of world knowledge across their lifetime because of reduced reading experience.
  • When assessing school-aged children with reading difficulties, it is essential that the assessment battery include both reading and oral language assessment tasks including tests of phonology, orthography (spelling), morphology, semantics, vocabulary, syntax and discourse processing.
  • Regardless of the label (or labels), intervention needs to be tailored to target each child’s strengths and weaknesses across all domains of language, in part because they all impact reading comprehension.
  • Everyone working in child literacy – parents, researchers, speech therapists, teachers, educational psychologists, and students themselves – need to know that dyslexia and DLD are distinct but often co-occurring disorders.

What do I do now?

Maximising children’s potential in the early years needs to empahsise the importance of oral language as a springboard for learning. It is crucial for educators to be monitoring the progress over time of a child who presents with poor language in the preschool years. Interventions in the early years should maximise the possibility of strengthening the oral foundations for literacy – not just reading readiness but also vocabulary and narrative skills. On the other hand, teachers and practitioners who work with children with dyslexia should recognise it is a language learning disorder and ensure language skills beyond phonology are considered both in assessment and intervention.

There is a lot that can be done at home to help with language development and communication skills. For more information about DLD, follow and support the wonderful work of;

We also recommend the free Progress Checker tools and information on communication development by age produced by ICAN (UK):

  • Progress Checker  – free, brief tool with questions to identify whether your child may have communication difficulties
  • Universally Speaking – free downloadable booklets detailing communication development from birth to 18 years

If you suspect DLD in your child, you can discuss this with your child’s teacher and seek the support of a Speech Language Therapist (SLT). There are SLT’s working in public service through the Ministry of Education (free), and also in private practice (paid services).

SLT’s are skilled at assessing all aspects of communication, providing intervention to develop those skills, and working with whānau and schools to help them support the child’s learning, social relationships, and growing independence. More information on SLT services in New Zealand can be found here:


Thank You 

The deb would like to thank Anna Kenno, Speech Language Therapist, for writing this document for the deb community.

This document was created Anna Kenno in February 2022