To Boost Kids' Vocabulary, We Need to Build Their Knowledge

It's impossible to directly teach students all the words they need to become proficient readers.

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Vocabulary is key to reading comprehension, and there are effective ways to teach it. But the only way to enable children to acquire the massive amount of vocabulary they need is to build their knowledge.

Having an extensive vocabulary generally means you’re a good reader, assuming you know how to decipher, or “decode,” written words. And if you read widely, you’re likely to acquire even more vocabulary—making you an even better reader.

For children who start out with a lot of vocabulary, that’s a virtuous cycle. But for others, it’s a cruel Catch-22: They don’t have the vocabulary that would enable them to read widely, which means they can’t engage in the very activity that would help them to acquire the vocabulary they need to become good readers.

It’s important to bear in mind that written texts use a greater number of unique words than spoken language—and those words are more sophisticated. So a student who has no trouble carrying on a conversation might still struggle with the vocabulary in books.

A study comparing oral language to written texts looked at a wide range of samples and found—according to reading expert Marilyn Jager Adams—that “without exception, the richness and complexity of the words used in the oral language samples paled in comparison with the written texts.” She adds that “of all the oral language samples evaluated, the only one that exceeded even preschool books in lexical range was expert witness testimony.”

Children who start school with large vocabularies typically pick up sophisticated words at home, usually because they come from highly educated families. Other children may be stumped by words used even in elementary-level texts.

Over 20 years ago, reading researcher Louisa Moats found that the kindergartners she was studying, who came from low-income families, got an average score in the fifth percentile on a commonly used test of oral vocabulary. When shown pictures to match words to, they were unable to come up with vocabulary like penguin, sewing, and parachute. By second and third grade they had moved up to the fifteenth percentile but still didn’t know words like amazed, locket, balcony, and weasel. “By fourth grade,” Moats wrote, “many students are clearly lost in the more complex text they encounter in school, even if their decoding skills are good.”

Unfortunately, the only thing that has changed in the last two decades is that fourth-graders are less likely to be expected to read complex text. Instead they’re limited to simple texts they can read on their own, on the theory that such an approach will equip them to read more complex texts. We’ve only postponed the day of reckoning to high school, where texts suddenly assume a lot of academic vocabulary many students don’t have.

Beyond Word Lists and Definitions

Elementary schools can and should explicitly teach children the kind of vocabulary words they’ll be expected to know at higher grade levels. But some approaches work better than others.

Building vocabulary isn’t just a matter of giving kids a list of words and definitions. A word is just the tip of an iceberg of knowledge. If kids learn a vocabulary word with no context, they might memorize the definition but they probably won’t truly understand its meaning or be able to use or remember it. And to really grasp and retain a new word, students need to encounter it not just in one context but repeatedly.

So, rather than reading books on random topics, which is the standard practice in elementary classrooms, students should be exposed to a series of texts organized around a single topic, over at least two or three weeks. The topics covered should also build on each other, so that when students move on to a new one they have most of the key vocabulary needed to understand it. In other words, the curriculum should be organized to systematically build knowledge. (The website of the Knowledge Matters Campaign has more information on that kind of curriculum.)

Vocabulary words that are taught directly should be drawn from texts in the curriculum—and teachers should introduce them by reading the texts aloud. That’s how it’s possible to break out of that Catch-22 that seems to prevent children from acquiring sophisticated vocabulary they don’t already have. Before they’re fluent readers, kids can take in more complex concepts and vocabulary through listening than through their own reading. Once they’ve heard a word a few times in meaningful contexts and, ideally, used it in class discussion, they’re more likely to understand it in texts they read independently.

A threshold question is which words in a text to target for instruction. A good curriculum will highlight them, but a general rule is to look for words that are commonly found in written but not spoken language—“Tier 2” words, according to a framework developed by researchers Isabel Beck, Margaret McKeown, and Linda Kucan. These include words like coincidence, absurd, and industrious. (Tier 1 includes common words that kids are likely to just pick up, like clock, and Tier 3 encompasses highly specialized words like isotope.)

In addition, it’s a good idea to focus on words that are important to understanding the text at hand or likely to appear again in texts students will be expected to read in the near future. Beyond providing an understandable definition, teachers can relate a word to other concepts—for example, comparing pond to lake and ocean—and explain its other meanings. Even a simple word like fan can have multiple meanings—a ceiling fan, a sports fan—or be used as a verb (“She fanned herself in the hot room”). With more sophisticated words or phrases like medieval or middle class, there are so many possible nuances that—as history teacher and blogger Michael Fordham has written—you need a “knowledge party in your head.”

Children Also Need to Learn Words They Haven’t Been Taught

But evidence tells us it’s impossible to directly teach children all the words they need to become fully literate. It’s been estimated that students need to learn around 100,000 words to understand the texts they’re expected to read in kindergarten through eighth grade. According to reading researcher Mark Seidenberg, children need to add about eight new words a day during their first several years of schooling.

That means kids need to acquire vocabulary they haven’t actually been taught. How can they do that? One possibility is to encourage them to look up words they don’t know. But, while students should be made aware of dictionaries and glossaries—and Google—they may not understand the definitions they find. And breaking off reading a text to look up words repeatedly makes comprehension more difficult.

Students can also be taught to use context to infer the meanings of unfamiliar words. But, according to researcher Marilyn Adams, that works only about 50% of the time. And the students who are best at inferring meanings are those who already have an extensive vocabulary—another Catch-22.

A more powerful strategy is to teach students about the meanings of components of the words they’re learning directly, like prefixes and suffixes, along with Greek and Latin roots. If they know that the un in unhappy means “not,” they’re more likely to understand a word like undistinguished. It’s also helpful to teach word families: if the target word is celebrity, for example, bring in words like celebrate and celebration.

Still, none of this fully explains how some students are able to acquire the vast number of words they need to be successful readers. According to both Adams and Seidenberg, a study involving a computer model that simulates the process of acquiring vocabulary provides insight into what actually happens.

As researchers fed texts into the model, the computer built associations between each word in a text and those surrounding it. As associations between the words and the contexts grew, networks of knowledge became activated that extended to some that the model had never “read.” In fact, according to Adams, “the amount the model learned about words that did not appear in a given reading was three times as much as what it learned about words that were in the reading.”

That makes sense, Adams continues, if we think about it in terms of acquiring knowledge rather than vocabulary. If students learn about, say, lions and tigers, they’ll also be acquiring general concepts and networks of words that apply to felines they haven’t learned about—say, lynxes. If they then read about lynxes, they’ll pretty much automatically have an understanding of what a lynx is.

Again, though, this process depends on systematically building children’s knowledge. Reading one book on lions or tigers is unlikely to enable students to absorb and retain the network of information that will support their understanding of words they haven’t been taught.

The bottom line is that “vocabulary” isn’t really distinct from “comprehension,” as a popular infographic suggests. And both aspects of literacy can only grow alongside knowledge. So if we want to boost students’ vocabulary—and their reading comprehension—we need to systematically build their knowledge.

This post originally appeared on Forbes.com.