#  Improving second-grade reading comprehension through a sustained content literacy intervention: A mixed-methods study examining the mediating role of domain-specific vocabulary 

 



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 **Date:** 01/15/2026 

 

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This mixed-methods study investigates how a sustained Tier 1 content literacy intervention improves second-grade students’ reading comprehension by building networks of domain-specific vocabulary knowledge over time. Drawing on data from a longitudinal randomized controlled trial involving 2,156 students across 30 schools, the authors use structural equation modeling to examine whether vocabulary learning in Grades 1 and 2 mediates the intervention’s effects on domain-specific reading comprehension in Grade 2. Results show that students’ cumulative domain-specific vocabulary knowledge explained 69% of the treatment effect on reading comprehension transfer, indicating that vocabulary growth is a primary mechanism through which content literacy instruction supports comprehension. Complementing the quantitative findings, teacher surveys and interviews reveal instructional practices that help deepen vocabulary learning, including repeated incidental exposure to words, teaching vocabulary in semantic networks through concept mapping, and connecting words to broader topics and prior knowledge. Together, the findings provide strong evidence that sustained, knowledge-building literacy instruction—paired with rich teacher vocabulary practices—can significantly strengthen students’ ability to comprehend complex informational texts.



 

 

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- [ Curriculum ](/focus-areas/curriculum)
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- [ K12 ](/sector/k12)