Specific language impairment (SLI) is a condition in which a child has significant difficulty learning and using language despite having normal hearing, typical intelligence, and no obvious neurological cause. It affects roughly 7% of children, or about 1 in 14. While the term SLI has been used for decades, a 2017 international consensus of 57 experts recommended replacing it with “developmental language disorder” (DLD), which is now the preferred term in clinical and research settings.
Why the Name Changed to Developmental Language Disorder
The shift from SLI to DLD wasn’t just cosmetic. The old label implied that language was the only area affected and that the disorder was neatly separated from other developmental differences. In practice, the boundaries between this condition and typical development are fuzzy, and many children with language difficulties also have challenges in other areas. The new term, DLD, is meant to function as a broader umbrella that captures the full range of unexplained language problems in children, without requiring a specific IQ threshold. Previously, a child needed to score in the normal range on nonverbal intelligence tests to qualify for an SLI diagnosis. The expert panel rejected that requirement, finding it unsupported by evidence.
DLD is not considered a specific syndrome with a single cause. It is a category designed to identify children who would benefit from speech and language therapy. The definition applies specifically to children whose language problems are expected to persist, not to those with temporary delays that resolve on their own.
What Language Difficulties Look Like
Children with this condition are typically late to start talking, and once they do, broad difficulties across multiple areas of language become apparent. The most consistent problems show up in vocabulary, grammar, and sentence structure, and these can persist well into the teenage years.
Grammar is often the most telling area of difficulty, especially for English-speaking children. Verbs give them particular trouble. In English, verbs carry markers that indicate tense and agreement: “she runs,” “she walked,” “she is running.” Children with DLD are significantly delayed in learning these markers and continue to leave them off long after their peers have mastered them. A child might say “she walk” instead of “she walked” or drop the helper verb entirely. These omission errors in spoken language can last until around age 8, while difficulty understanding these same structures in other people’s speech may continue into adolescence. The slow pace of learning in this area, not just the delay but the reduced rate of growth, is what distinguishes DLD from a simple late start.
How It Differs From Autism
Language problems appear in both DLD and autism, but the nature of the problems is different. Children with DLD struggle primarily with the structural building blocks of language: sounds, word forms, and sentence construction. A child with DLD might have trouble forming a grammatically correct sentence but use language appropriately in social situations, such as taking turns in conversation or adjusting their tone depending on who they’re talking to.
Children with autism, by contrast, tend to have their most striking difficulties with pragmatics, the social use of language. They may speak in grammatically complete sentences but struggle with things like understanding sarcasm, reading conversational cues, or knowing when to change the subject. The two conditions can overlap, and some researchers have debated whether they sit on a continuum, but this structural-versus-social distinction remains a key part of how clinicians tell them apart.
Genetics and Heritability
DLD runs in families. One of the best-studied genetic links involves the FOXP2 gene, which provides instructions for a protein that controls the activity of other genes involved in brain development. Variants in FOXP2 cause a specific speech and language disorder inherited in an autosomal dominant pattern, meaning a child only needs one copy of the altered gene to be affected. In about half of known cases, the genetic change is new and wasn’t inherited from either parent, arising spontaneously during early development.
FOXP2 is not “the language gene,” though. DLD is complex and multifactorial, meaning many genes likely contribute small effects rather than a single gene explaining the whole picture. The condition varies widely from child to child, which is consistent with this kind of genetic architecture.
Co-occurring Conditions
Children with DLD frequently have other developmental challenges. Reading difficulties are common, which makes sense given that the grammar and vocabulary weaknesses that define DLD also underpin reading comprehension and decoding. ADHD overlaps with reading disabilities at notable rates: 15 to 50% of children with ADHD also meet criteria for a reading disability diagnosis, and vice versa. Because DLD, reading difficulties, and attention problems share overlapping cognitive demands, a child may carry more than one diagnosis at a time.
How It’s Identified
Speech-language pathologists assess DLD using standardized language tests that measure a child’s abilities across vocabulary, grammar, sentence comprehension, and expressive language. These assessments compare a child’s performance to what’s expected for their age. No single test confirms or rules out DLD. Clinicians look at the overall pattern: how a child speaks, how well they understand what others say, and whether their difficulties are significant enough to interfere with daily communication and learning. Because the condition is defined by persistent problems, a clinician will also consider whether difficulties have been present over time rather than reflecting a temporary setback.
What Therapy Involves
The core treatment for DLD is speech and language therapy, and the evidence for its effectiveness is generally positive. Therapists use several overlapping techniques. Modeling involves the therapist producing correct language forms during play or conversation so the child hears them repeatedly in natural contexts. Sentence recasting is a related approach where the therapist takes something the child has said incorrectly and immediately repeats it back in corrected form without directly pointing out the error. If a child says “her runned fast,” the therapist might respond, “Yes, she ran fast!” Imitation-based activities ask the child to practice producing specific words or sentence structures.
Research on these approaches shows that most children who receive therapy improve in measurable ways. Studies report increases in vocabulary use, more complex and diverse sentence structures, more verbal communication during play, and improvements in expressive language skills overall. The specific techniques used vary depending on a child’s age and the particular language areas that need the most support, but the overall direction of the evidence is encouraging.
Long-Term Outlook
DLD is not something most children simply outgrow. It has lifelong implications. Children with DLD tend to achieve lower academic outcomes, and as adults, they are more likely to obtain lower vocational qualifications and work in less skilled occupations compared to peers without language difficulties. This doesn’t mean outcomes are fixed. Early and sustained intervention can change a child’s trajectory. But the persistence of the condition, especially for grammar and comprehension, means that support often needs to continue well beyond early childhood and into the school years, where language demands increase sharply as children are expected to read textbooks, write essays, and follow complex verbal instructions.