Preadolescents and adolescents with language disorders struggle to understand the types of sentences they are exposed to at secondary school. Academic language, or informational language is characterized by long, complex sentences and technical vocabulary, used to express higher level ideas (for more information about this type of language, see my blog post: https://secondaryschoolslt.wordpress.com/2026/04/15/what-is-expository-discourse-and-how-is-it-relevant-at-secondary-school/).
Many students with Developmental Language Disorder (DLD) have restricted vocabularies which impede their understanding of this type of language. They are also likely to have weaker, or nonexistent knowledge of certain grammatical structures that cause no problems for their peers, such as passives and object relative clauses (Scott, 2009, Montgomery et al, 2021).
However, not even their typically developing peers can be expected to understand all of the sentences they come across at this age, since not all adults achieve complete mastery of certain sentence structures. For example, in one study, Nippold et al (2020) found that only 25% of the supposedly typical young adults in their sample were able to produce past tense counterfactual (PTCF) sentences perfectly, and only 50% were able to understand them all the time.
Aspects other than linguistic knowledge also affect our understanding of such sentences. For example, Leonard et al (2007) found that 62% of the variance in children’s composite language scores was down to nonlinguistic factors, such as Verbal Working Memory (VWM) and processing speed.
According to Balthazar and Scott (2023, p.567), “syntactic complexity carries a processing cost for all speakers across all modalities”. You might imagine that written language would be less affected by factors such as VWM than oral language which must be interpreted in the moment. However, this has not been found to be the case, probably because the reader still has to use their inner voice to “re-auditorise” the sentence and move parts around.
Researchers such as Scott, Balthazar and Nippold have spoken in detail about exactly what makes sentences more complex and harder to process. Scott (2009) highlights factors such as the number propositions and embeddings, the sentence order as well as the distance between the main elements. In a later article, Balthazar and Scott (2023, p. 565) defined sentence complexity as “any structure that adds to, interrupts, or changes the subject–verb–object (SVO) order within a clause or adds clauses within a sentence and can be reasonably predicted to increase the processing “load” of the sentence”.
Firstly, then, a long sentence made up of multiple clauses is harder to process than a simple sentence made up of just one main clause. By definition, a sentence becomes “compound” or “complex” when coordinated or subordinate clauses are added. Syntactic complexity is not just about the length of the sentence, but also the “clausal density” or “subordination index”; in other words, the average number of clauses per sentence.
Similarly, it is not just about the number of clauses, but how they are arranged. Academic text tends to feature “different levels of subordination” to express a hierarchy of ideas. Conjunctions such as “unless”, “despite” and “otherwise” are used to give weight to certain ideas over others and are capable of expressing subtle relationships between different parts of a sentence.
This contrasts with oral, conversational language where conjoined clauses of equal value connected with simple conjunctions such as “and”, “but” and “so” are more common (see my post: https://secondaryschoolslt.wordpress.com/2026/04/06/how-are-oral-and-written-language-different/ for more about the differences between oral and written language).
A particularly complex form of subordination is called “embedding”, where one clause is placed within another, and acts as a noun or adjective in that sentence. Central embedding is considered particularly difficult to understand, and “nesting”, where one clause is placed within another within another even more so. When this exceeds three levels, the sentence quickly becomes unintelligible, e.g. “the dog the cat the mouse bit chased barked”.
Syntactic complexity can also be increased through elaboration of noun and verb phrases. In one study, Leonard et al (2013) found that when adjectives were added to different nouns, e.g. “the happy yellow dog washes the little pig”, children with language disorders quickly became confused about who was the agent and who was the patient (Leonard et al, 2013, p. 12).
Cheryl Scott (2009, p. 186) also compares the simple sentence “the amendment was a disaster” with the more complex sentence, “the thoroughly rewritten and meaningless amendment that was inserted by the aide was a disaster.” Whilst both sentences contain the same subject, amendment, the second has been expanded through the use of modifiers which come before the noun, “pre-modifying” it, as well as a relative clause which comes afterwards, “post-modifying” it.
Sentences such as this, where a large amount of information precedes the main verb, can also be referred to as “left-branching”. According to Marilyn Nippold (2023, p.44), the entire noun phrase must be held in working memory until the reader/ listener reaches the main action, “was a disaster” and finds out what the sentence is about, increasing processing demands. Other structures which may feature in left branching sentences include adverbial clauses, prepositional phrases and appositives.
English is also a language with a strict subject-verb-object (SVO) order, and anything which disrupts this is thought to make sentences harder to understand. As mentioned, pre- and post-modification of the noun phrase can do this by creating gaps (long distance dependencies) between elements which are typically close together. However, any sentence which is not in canonical (typical) order, such as passives and clefts (Scott and Balthazar, 2013) may cause difficulties, since certain elements need to be moved around in the mind.
One further point is that students with DLD may also be overly reliant on immature comprehension strategies such as order-of-mention and context cues. Referring back to the last example sentence, a student with a language disorder may mistakenly connect the predicate “was a disaster” with the immediately preceding noun, “aide”, leading them to the conclusion that the aide was the disaster rather than the amendment. This mistake of believing the nearest noun to be the subject of the sentence is not uncommon (Scott, 2009, Scott and Balthazar, 2013).
Finally, studies have shown that sentence complexity impacts working memory performance differently across different languages. In English, syntactic complexity had the greater impact, whilst in Hungarian, it was the increased morphological complexity of words (Kail and Csépe, 2006). This is likely due to the distinguishing features of the different languages.
To sum up, some sentences are so complex that they challenge the processing limits of any listener or reader. As students progress through secondary school and beyond, they are increasingly exposed to this type of academic language. Knowing exactly what can make sentences hard to understand, for all of us, not just those with language disorders will make it easier for us to support our students.
Notes
Balthazar, Catherine H., and Cheryl M. Scott. “Sentences Are Key.” American Journal of Speech-Language Pathology 33, no. 2 (2023): 564–579.
Kail, Michèle, Valéria Csépe, F. L. C. C. 2006. “Effects of Sentence Length and Complexity on Working Memory Performance in Hungarian Children with Specific Language Impairment: A Cross-Linguistic Comparison.” [International Journal of Language & Communication Disorders] 41, no. 6: 713-731.
Leonard, Laurence B., Patricia Deevy, James W. Miller, Chrystal Rameela, Robert Schwartz, and J. Bruce Tomblin. “Speed of Processing, Working Memory, and Language Impairment in Children.” Journal of Speech, Language, and Hearing Research 50, no. 2 (April 2007): 408–428.
Leonard, Laurence B., Patricia Deevy, Marc E. Fey, and Shelley L. Bredin-Oja. “Sentence Comprehension in Specific Language Impairment: A Task Designed to Distinguish between Cognitive Capacity and Syntactic Complexity.” Journal of Speech, Language, and Hearing Research 56, no. 3 (June 2013): 937–949.
Montgomery, James W., Ronald B. Gillam, and Julia L. Evans. “A New Memory Perspective on the Sentence Comprehension Deficits of School-Age Children With Developmental Language Disorder: Implications for Theory, Assessment, and Intervention.” Language, Speech, and Hearing Services in Schools 52, no. 2 (April 2021): 449–466.
Nippold, Marilyn A., Abigail Nehls-Lowe, and Daemion Lee. “Development of Past Tense Counterfactual Sentences: Examining Production and Comprehension in Adolescents and Adults.” Journal of Speech, Language, and Hearing Research 63, no. 10 (October 2020): 3474–3484.
Nippold, M.A. (2023). Grammar guide for speech-language pathologists: Steps to analyzing complex syntax. San Diego: Plural Publishing.
Scott, Cheryl M. “A Case for the Sentence in Reading Comprehension.” Language, Speech, and Hearing Services in Schools 40, no. 2 (2009): 184-191.
Scott, Cheryl M., and Catherine H. Balthazar. “The Grammar of Information: Challenges for Older Students With Language Impairments.” Topics in Language Disorders 30, no. 4 (2010): 288–307.
Scott, Cheryl M., and Catherine Balthazar. “The Role of Complex Sentence Knowledge in Children with Reading and Writing Difficulties.” Perspectives on Language and Literacy 39, no. 3 (Summer 2013): 18–3
Thoughts of a secondary school SLT 