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Vocabulary and Sight Word Instruction

Over the years, I have written pretty extensively about the problems with a Whole Language approach vs a phonics approach. Ultimately, we see Whole Language programs fail, likely, because there are just too many words in the English language for it to be efficient to teach students how to read via purely rote memorization. However, scientific truth is rarely fully displayed in binary truths and the question does beg is there ever a place for individual words to be taught specifically to students, either for fluency purposes or comprehension purposes. 


I can personally think of two cases in which it might make sense to explicitly and systematically teach students individual words: high-frequency, irregularly spelled words, and content vocabulary words. High-frequency, irregularly spelled words are often touted as best taught via memorization, as they cannot be easily decoded, from just regular phonics instruction. Whereas, content specific vocabulary is often taught specifically in the later elementary grades, where phonics has been shown to be less effective. This approach has been specifically advocated for by proponents of CKLA and Amplify. That being said, the approach to these two types of vocabulary instruction is often very different. While irregular words are often taught through rote memorization, with an emphasis on increasing fluency, content words are often taught with an emphasis on meaning. 


I must admit, I am especially curious about the instruction of the irregular words, as it seems a more crucial question to answer for our struggling readers. The esteemed Dr. Timothy Shanahan recently wrote about this topic in a blog and he suggested that there are 100 commonly used words that can be best taught through rote memorization. These 100 words are the most frequently used words and can account for up to 50% of all words students read in texts. However, I have noticed that there is not a strong consensus within the Science of Reading community on the issue of irregular words. 


While, Dr. Shanahan advocates teaching them via memorization; other scholars have pointed out that these words can be still decoded with additional phonics instruction. Dr. Pete Bowers has suggested to me that these words are not actually irregular and are spelled based on morphological roots; moreover, that these words are best taught via morphology instruction. More recently, I have noticed many influencers within the Science of Reading space, suggesting that we use the Heart Words technique to teach these words. With the heart word method, teachers place a heart over the parts of a word that are not easily decoded to indicate that students should memorize these words by heart. While personally, I have always taught irregular words via rote memorization, I think it is important to critically examine what the scientific literature shows us, before jumping to any conclusions as to what is best practice. Moreover, I think there are rational arguments that can be made for any of the above described teaching methods. However, I think this fact just makes it even more important to defer to the scientific literature. 


Unfortunately, the scientific literature does not appear to be quite clear at this point. I was able to find 8 meta-analyses on the topic of teaching reading vocabulary. Showing a mean effect size of .70. Which is very significant, in terms of reading studies. However, none of these meta-analyses specifically focused on high-frequency irregular spelled words.

While there was one meta-analysis specifically on “sight word” instruction (a muddling term), by Dr.  Diane Browder, the meta-analysis only looked at p-values and did not examine effect sizes. This meta-analysis can therefore not reliably tell us the impact of directly teaching “sight words” or the best way to teach them. One meta-analysis that might help however, was the 2010 meta-analysis by Dr. Loren Marulis, which specifically focused on vocabulary instruction in pre-kindergarten to grade 1. This meta-analysis included 67 studies and showed very high results. 

There were several very fascinating possible take-aways from this study. Firstly, vocabulary instruction in the primary grades was especially high yield. Indeed the effect sizes found for vocabulary here are higher than the effect sizes generally found for phonics, in the primary grades. While we know from other research that Whole Language approaches do not work, it does appear that we still need to teach some words, individually and directly. Secondly, while explicit instruction was unsurprisingly superior to implicit instruction (defined by the author as natural reading experiences), a combined approach (defined by the author as pairing actual reading practice with explicit vocabulary instruction) showed higher results than a purely implicit or explicit approach. I must say this confirms a personal bias of mine, as I have always found reading instruction worked best, when students received both reading practice time and explicit instruction. 


Also interesting, was the particularly high results found for teaching vocabulary to at-risk readers, which is significantly higher than the impacts of teaching phonics to at-risk readers. I think this result suggests that it is crucial that we teach both phonics and vocabulary to struggling readers. On this topic the authors wrote, ““There is no causal link between vocabulary and comprehension, (b) vocabulary instruction does not transfer beyond the taught target words and texts in which it is learned [......] Poor readers are likely to have difficulties with lower level skills such as decoding and quick access to word meanings (Mezynski, 1983). If students learn target words contained in the text, it may free up cognitive resources that can be allocated for higher level processes of integrating text (Mezynski, 1983; Perfetti, 1985). In comparison to students who do not have lower level deficits, poor readers will likely benefit more from learning vocabulary, because they can access words more quickly, thus alleviating cognitive resources and increasing their capacity to engage in the higher level skills required for comprehension.” (Marulis, 2010). 


However, absolutely crucial to this conversation was the impact of time on these results. As the authors found that vocabulary instruction showed very quickly diminishing returns. Indeed, the authors found the highest results for studies that included 5 or less instructional sessions and the lowest results for more than 18 sessions. While all results were high, there was clearly a direct correlative relationship, in which more time spent on vocabulary instruction meant lower results. With this in mind, I think it might be logical for teachers to teach the high frequency, irregularly spelled words and to move on. 


I think the 2009 meta-analysis by Dr. Amy Elleman, Et, al. Is very interesting in comparison to the Marulis study. This meta-analysis looked at 37 kindergarten to grade 12 studies, and specifically focused on comprehension outcomes. Their study found a mean effect size of .10 on reading comprehension results for teaching vocabulary. This was the only vocabulary meta-analysis that focused on comprehension. Moreover, it looked at higher grades than the other studies. For this reason, I think it is fair to say that the research evidence for teaching extended vocabulary, vocabulary in the later grades, or for comprehension purposes, appears weaker. Theoretically I think it makes more sense to teach vocabulary comprehension through morphology, however, the research evidence is also weak in this regard. My secondary meta-analysis of morphology instruction showed a mean ES of .18 for comprehension outcomes. That being said, the Elleman meta-analysis did show greater effect sizes for at-risk readers, with a mean impact of 1.23, further reinforcing the fact that vocabulary instruction appears to have a strong impact for struggling readers. Similarly to the Ellman and Marulis meta-analyses, the 1990 Marmolejo, the 1987 Foster and the 1986 Arnold meta-analyses also showed higher effect sizes for teaching vocabulary to struggling and disabled readers. 

As you can see from the above chart, the impact of vocabulary instruction for struggling readers is very high. For comparison, the NRP phonics meta-analysis found a mean effect size of .44 for struggling and disabled readers, my phonics meta-analysis also found a mean ES of .44 for struggling and disabled readers, and my secondary meta-analysis of morphology instruction found a mean ES of .55 for struggling readers. 


With all of this in mind, I think a couple of practical recommendations can be made based on the current state of the scientific literature. Vocabulary instruction should be limited, however, is likely necessary in the primary grades, and for struggling readers. That being said, I do not think we currently have enough research to definitively answer several important questions, including: How best should the 100 most commonly used words be taught, what is the impact of teaching vocabulary in different grades, how much vocabulary instruction is too much. This is important to keep in mind, as I think it shows that recommendations made in this regard are likely to be theoretical and not scientifically based.

Witten by Nathaniel Hansford

Last Edited, 2022-05-3


T, Shanahan. (2022). Should I teach students to memorize sight words and monitor their progress? Shanahan On Literacy. Retrieved from <>. 


Marulis, Loren & Neuman, Susan. (2010). The Effects of Vocabulary Intervention on Young Children’s Word Learning A Meta-Analysis. Review of Educational Research. 80. 300-335. 10.3102/0034654310377087. 

Browder, Diane & Xin, Yan Ping. (1998). A Meta-Analysis and Review of Sight Word Research and Its Implications for Teaching Functional Reading to Individuals with Moderate and Severe Disabilities. The Journal of Special Education. 32. 130-153. 10.1177/002246699803200301. 


Elleman, Amy & Lindo, Endia & Morphy, Paul & Compton, Donald. (2009). The Impact of Vocabulary Instruction on Passage-Level Comprehension of School-Age Children: A Meta-Analysis. Journal of Research on Educational Effectiveness. 2. 1-44. 10.1080/19345740802539200. 


J, Hattie. (2022). Vocabulary Instruction. Visible Learning Metax. Retrieved from <>. 



Browder DM, Xin YP. A Meta-Analysis and Review of Sight Word Research and Its Implications for Teaching Functional Reading to Individuals with Moderate and Severe Disabilities. The Journal of Special Education. 1998;32(3):130-153. doi:10.1177/002246699803200301

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