Dyslexia and Developmental Language Disorder: Understanding the Difference and the Overlap

When a child finds reading difficult, dyslexia may be one of the first explanations parents consider. But reading involves several skills, and understanding the difficulty means looking beyond how accurately a child reads the words.

Can they understand the vocabulary? Follow the sentences? Explain what has happened in the story? Do similar difficulties arise when someone reads the text to them?

These questions help us consider both literacy and language.

Dyslexia and developmental language disorder (DLD) are distinct conditions. A person can have either one separately, or both together. Recognising that overlap matters because support needs to address the whole picture.

What is dyslexia?

Dyslexia involves persistent difficulties with developing reading and spelling skills.

Some people find accurate word reading difficult. Others read accurately but slowly or with considerable effort. Spelling may remain difficult even when reading has improved.

These difficulties can affect access to written information and how manageable schoolwork, study or workplace tasks feel.

A dyslexia assessment considers the person’s history, current literacy skills, relevant processing skills and the wider evidence. A single difficulty or test score does not establish a diagnosis.

What is developmental language disorder?

Developmental language disorder involves persistent difficulties with understanding and/or using language that affect everyday communication or learning.

A person may find it difficult to understand complex sentences, learn vocabulary, explain ideas clearly or organise a spoken account of an event.

DLD is not simply about unclear pronunciation. Someone may speak clearly while still finding aspects of language difficult.

Language needs are investigated by a speech and language therapist. They consider the person’s development and communication across relevant situations.

How do dyslexia and DLD differ?

A useful starting point is that dyslexia primarily concerns reading and spelling development, while DLD concerns broader language development.

However, spoken and written language are closely connected. The difficulties can overlap, and a simple checklist cannot reliably separate them.

For example, difficulty understanding a written passage might arise because reading the words is effortful, because the language is difficult to understand, or because both are happening.

We need to investigate what is contributing to the difficulty rather than assume that every reading problem has the same explanation.

Can someone have dyslexia and DLD together?

Yes. Having DLD does not rule out dyslexia, and having dyslexia does not rule out DLD.

A child may have persistent difficulties learning to read and spell alongside difficulties with vocabulary, sentence structure or understanding spoken language.

Equally, someone can have dyslexia without DLD, or DLD without dyslexia.

This is why it is important to consider literacy and language together while recognising their differences. One diagnosis should not bring the investigation of other significant concerns to an end.

Why does reading comprehension need careful consideration?

Understanding a text involves reading the words and understanding the language and ideas they convey.

If a child uses considerable effort to work out the words, following the meaning may become harder. Another child may read the words accurately but struggle to understand unfamiliar vocabulary or how the sentences fit together.

Reading a passage aloud to the child can provide useful information about what changes when the word-reading demand is reduced. However, this is an observation to explore, rather than a diagnostic test.

The topic, vocabulary, background knowledge and complexity of the text also matter.

What might parents and teachers notice?

Language concerns may become apparent when a child:

• Finds spoken explanations difficult to follow.

• Struggles to learn or use new vocabulary.

• Has difficulty explaining an event in a way others can follow.

• Finds complex questions or sentences difficult to understand.

• Needs substantial help to put ideas into words.

Literacy concerns might include persistent difficulties sounding out unfamiliar words, slow reading or spelling difficulties despite teaching and practice.

These observations are helpful starting points. They do not tell us, on their own, whether the child has dyslexia, DLD, both or another explanation for their difficulties.

What if my child is already seeing a speech and language therapist?

Share their reports and recommendations with school and with any assessor investigating literacy concerns.

Information about language development, the support provided and current needs can help build a more complete understanding.

If reading and spelling difficulties persist, it is reasonable to ask whether these have been investigated in their own right. They should not automatically be attributed entirely to an existing language diagnosis.

Similarly, if a child with dyslexia has significant difficulty understanding or using spoken language, those concerns deserve attention too.

What support might be needed?

Support should follow the individual’s needs.

A child with persistent word-reading and spelling difficulties may need explicit, structured literacy teaching. A child with language difficulties may need teaching that develops vocabulary, sentence understanding and ways of expressing ideas, informed by speech and language therapy advice.

Someone with both may need a coordinated combination.

For example, learning a new curriculum word might involve exploring its meaning, practising its pronunciation, discussing its use in sentences and teaching its spelling.

The aim is to make the different elements of support work together.

What can I discuss with school?

Ask the teacher and SENCo to explain where the difficulty appears.

Useful questions include:

• How does my child read unfamiliar words?

• Is reading accurate, fluent and manageable?

• What happens when someone reads the material to them?

• How well do they understand spoken explanations?

• Which vocabulary or sentence structures cause difficulty?

• What support is in place, and how is progress being reviewed?

• Would advice from a speech and language therapist be useful?

Share examples from home too. A child’s experience during a conversation or homework task can add information that is not obvious from their finished work.

Appropriate support should not wait until every question about diagnosis has been resolved.

How can we protect confidence?

Children may not understand why they find an instruction, conversation or reading task difficult. They may assume that everyone else understands immediately and that needing help means they are less capable.

Give them time, check understanding sensitively and avoid treating difficulty as unwillingness.

Rather than saying, “You weren’t listening”, try asking which part was unclear and explaining it differently.

Make it safe to ask for clarification. A child should not feel that they need to hide confusion to avoid embarrassment.

For adults, the same principle applies: needing clearer language, additional time or a different presentation of information should not become a judgement about ability or effort.

How can a dyslexia assessment help?

A dyslexia assessment investigates reading and spelling difficulties while considering relevant language information and the broader developmental and educational history.

It can identify concerns that warrant further investigation, but it does not replace a specialist speech and language assessment or establish DLD.

Where another professional’s input is needed, an onward referral may be recommended. Existing reports can also help professionals coordinate their understanding and advice.

The aim is to explain the person’s needs carefully and provide useful next steps, including when more than one area requires support.

Understanding the whole picture

The most helpful question is not simply, “Is this dyslexia or DLD?”

It is, “What is this person finding difficult, what is contributing to that difficulty, and what support would help?”

Sometimes the answer involves dyslexia, sometimes DLD, and sometimes both. Whatever the explanation, the person deserves understanding and support that reflects their individual experience.

Every child's profile is different, and a careful assessment looks at the whole picture rather than a checklist of signs. If you're interested in a dyslexia assessment in Cornwall and want to understand how your child learns, take a look at what a dyslexia assessment involves or book a free call.

You can also explore my free courses, videos and self-help guides for more information about dyslexia and related topics.

Further reading

The Royal College of Speech and Language Therapists provides information about DLD.

Research by Snowling and colleagues explores dyslexia and DLD as distinct conditions that can co-occur and affect reading comprehension.