Why Strong Decoders Can Still Struggle with Comprehension

Teachers often encounter students who can read nearly anything placed in front of them but struggle to explain what they’ve read. These students read accurately and fluently, so it feels as though comprehension should follow automatically. Research, however, tells us otherwise. While decoding is essential, it is only one component of what students need to truly understand text (Gough & Tunmer, 1986; Perfetti, Landi, & Oakhill, 2005).

Decoding gets students through the door—but it doesn’t finish the job

The Simple View of Reading explains that reading comprehension is the product of two components working together:

• Decoding: accurately and efficiently reading the words on the page

• Language comprehension: understanding spoken language, including vocabulary, sentence structure, and meaning (Gough & Tunmer, 1986)

  
  

Once students reach a reasonable level of decoding proficiency, additional phonics or fluency practice alone does not resolve comprehension difficulties. At that point, the primary barriers are typically language and knowledge—not word reading (Catts, Hogan, & Adlof, 2005; Tilstra et al., 2009). This explains why a student may read a passage aloud smoothly and then struggle to answer a simple question such as, “What was this mostly about?”

When language and vocabulary are the real barriers

Many students who appear to be “good decoders” have underlying gaps in oral language and vocabulary. They may be able to pronounce words like consequence, reluctant, or proposal, yet lack a deep understanding of what those words mean. When too many words in a text are only partially understood, students are unable to build a coherent mental model of the text—even though they can read every word accurately (Perfetti et al., 2005).

Sentence structure adds another layer of complexity. As texts become more sophisticated, sentences grow longer and denser, often including embedded clauses, passive voice, and multiple ideas packed into a single sentence. Students may read these sentences fluently without tracking who did what, when, or why. By the upper elementary and secondary grades, language and vocabulary knowledge often explain more variance in comprehension than decoding skill alone (Catts et al., 2005).

Background knowledge: the “Velcro” for comprehension

Background knowledge functions like Velcro for new learning—the more students already know, the more new information sticks. Two students with similar decoding skills can read the same passage, yet the student with more topic knowledge will understand and retain significantly more (Oakhill, Cain, & Elbro, 2015).

When students approach a text with limited background knowledge, they must juggle unfamiliar vocabulary, new concepts, and new relationships all at once. Cognitive energy is spent simply trying to keep up, leaving little capacity for deeper comprehension skills such as inferring, summarizing, or integrating ideas. Instruction that intentionally builds knowledge over time—through connected texts and content-rich units—makes comprehension more accessible, even when decoding skill remains unchanged (Cabell & Hwang, 2020; Shanahan, 2020).

Comprehension habits: how skilled readers think

Strong comprehenders actively monitor their understanding as they read. They:

• Notice when meaning breaks down

• Slow down, reread, and ask questions

• Track how ideas connect across sentences and paragraphs (Oakhill et al., 2015)

  
  

Students who struggle with comprehension often have not received sufficient modeling or guided practice in these habits. Reading becomes an exercise in “getting through the text” rather than constructing meaning. Strategy instruction is most effective when embedded in authentic reading tasks with clear purposes—such as preparing for discussion, answering meaningful questions, or writing about learning—rather than isolated worksheet practice (Shanahan, 2020).

Implications for classroom instruction

For students who decode accurately but struggle to understand what they read, additional phonics instruction alone is unlikely to address the root of the problem. Effective instruction must intentionally support:

• Language: daily opportunities for rich oral language, interactive read-alouds, explicit vocabulary instruction, and exposure to complex sentence structures

• Knowledge: content-rich instruction that allows students to build and deepen understanding within topics over time

• Comprehension processes: explicit modeling and practice in monitoring understanding, connecting ideas, and summarizing meaning (Castles, Rastle, & Nation, 2018; Shanahan, 2020)

Current science-of-reading research consistently points to a both-and approach: strong early decoding instruction paired with sustained, intentional work in language, knowledge building, and comprehension. When these elements work together, students move beyond simply saying the words to truly understanding, applying, and enjoying what they read (Castles et al., 2018).

References

Cabell, S. Q., & Hwang, H. (2020). Building content knowledge to boost comprehension in the elementary grades. The Reading Teacher, 74(1), 79–88.

Castles, A., Rastle, K., & Nation, K. (2018). Ending the reading wars: Reading acquisition from novice to expert. Psychological Science in the Public Interest, 19(1), 5–51.

Catts, H. W., Hogan, T. P., & Adlof, S. M. (2005). Developmental changes in reading and reading disabilities. Current Directions in Psychological Science, 14(5), 255–259.

Gough, P. B., & Tunmer, W. E. (1986). Decoding, reading, and reading disability. Remedial and Special Education, 7(1), 6–10.

Oakhill, J., Cain, K., & Elbro, C. (2015). Understanding and teaching reading comprehension: A handbook. Routledge.

Perfetti, C. A., Landi, N., & Oakhill, J. (2005). The acquisition of reading comprehension skill. In M. J. Snowling & C. Hulme (Eds.), The science of reading: A handbook (pp. 227–247). Blackwell.

Shanahan, T. (2020). What is the role of background knowledge in reading? Reading Research Quarterly, 55(S1), S229–S243.

Tilstra, J., McMaster, K., Van den Broek, P., Kendeou, P., & Rapp, D. (2009). Simple but complex: Components of the Simple View of Reading across grade levels. Journal of Research in Reading, 32(4), 383–401.