Andrew Biemiller and Naomi Slonim (Biemiller, 2005, 2012; Biemiller & Slonim, 2001) reported similar research:
By the end of grade 2, children in the lowest vocabulary quartile had acquired slightly more than 1.5 root words a day over 7 years, for a total of about 4,000 root word meanings. In contrast, children in the highest quartile had acquired more than 3 root words a day, for a total of about 8,000 root word meanings. (Biemiller, 2012, p. 34)
According to Loren Marulis and Susan Neuman (2010), a slower rate of learning new words leads to a “cumulative disadvantage over time” (p. 301). Here we review three areas affected by this disadvantage: (1) reading ability, (2) independent reading, and (3) mental processes.
Vocabulary and Reading Ability
The nature of the cumulative disadvantage described by Marulis and Neuman (2010) becomes clear when one considers vocabulary’s effects on learning to read and reading comprehension. Michael Kamil and Elfrieda Hiebert (2005) described the process of learning to read as follows:
Beginning reading instruction is typically accomplished by teaching children a set of rules to decode printed words to speech. If the words are present in the child’s oral vocabulary, comprehension should occur as the child decodes and monitors the oral representations. However, if the print vocabulary is more complex than the child’s oral vocabulary, comprehension will not occur. (p. 3)
Students who have large oral vocabularies will recognize and understand more of the words they are asked to decode, which in turn allows them to more fully comprehend the passages they read. The importance of vocabulary knowledge in learning to read was emphasized by the National Reading Panel’s (NRP) 2000 report, Teaching Children to Read: An Evidence-Based Assessment of the Scientific Research Literature on Reading and Its Implications for Reading Instruction. Concerning vocabulary, the NRP (2000) reported:
Benefits in understanding text by applying letter-sound correspondences to printed material come about only if the target word is in the learner’s oral vocabulary. When the word is not in the learner’s oral vocabulary, it will not be understood when it occurs in print. Vocabulary occupies an important middle ground in learning to read. Oral vocabulary is a key to learning to make the transition from oral to written forms. (ch. 4, p. 3, italics added)
As seen in the NRP’s report and echoed by the authors of the CCSS, “the importance of students acquiring a rich and varied vocabulary cannot be overstated” (NGA & CCSSO, 2010a, p. 32).
Vocabulary and Independent Reading
A large vocabulary helps children learn to read; because of the connections between vocabulary and reading comprehension, students with large vocabularies are more successful readers and therefore more likely to read independently than students with smaller vocabularies. Steven Stahl (1999) described how this relationship affects the amount of reading that students do as they progress through school:
Because poor readers tend to read less than better readers, the gap between good and poor readers in absolute numbers of words read becomes progressively greater as the child advances through school…. Children who are good readers become better readers because they read more and also more challenging texts, but poor readers get relatively worse because they read less and also less challenging texts. Indeed, researchers have found large differences in the amount of free reading that good and poor readers do in and out of the school. (p. 12)
In other words, students who read well tend to read more, thus improving their vocabularies and reading skills, while students who have trouble reading tend to read less, thus missing opportunities to augment their vocabularies and improve their reading skills through practice. Much additional research supports the correlation between vocabulary level and reading comprehension (for example, Coyne, Capozzoli-Oldham, & Simmons, 2012; Cromley & Azevedo, 2007; Lesaux & Kieffer, 2010; Stahl & Nagy, 2006). In sum, the effects of vocabulary knowledge on reading comprehension and skill are significant and long lasting.
Vocabulary and Mental Processes
Vocabulary is also related to basic mental processes and skills that affect students’ overall academic achievement. Katherine Stahl and Steven Stahl (2012) explained that “children’s ability to name things establishes their ability to form categories” (p. 72). For example, a student who learns the word shake can subsequently attach other words and concepts to it, such as shiver, vibrate, wiggle, flutter, jitter, and so on. As students develop more complex categorization systems for new words, they are better able to summarize (Kintsch, 1998; Kintsch & van Dijk, 1978) and make inferences (Anderson & Pearson, 1984) about new information. Stahl and Stahl (2012) concluded that “to expand a child’s vocabulary is to teach that child to think about the world, and in a reciprocal fashion, [a] more refined vocabulary indicates that child’s degree of knowledge about his or her world” (p. 73). Essentially, knowing more words allows students to think about more concepts in more ways.
Researchers have also found that there is a significant correlation between vocabulary and intelligence. Joseph Jenkins, Marcy Stein, and Katherine Wysocki (1984) cited correlations as high as 0.80 between vocabulary and intelligence, and Marzano (2004) summarized similarly high correlations between vocabulary knowledge and intelligence, as shown in table 1.2.
Table 1.2: Correlations Between Vocabulary and Intelligence in Various Studies
| Study | Correlation |
| Terman (1918) | 0.91 |
| Mahan and Whitmer (1936) | 0.87 |
| Spache (1943) | 0.92 |
| Elwood (1939) | 0.98 |
| McNemar (1942) | 0.86 |
| Lewinski (1948) | 0.82 |
| Wechsler (1949) | 0.78 |
| Raven (1948) | 0.93 |
Source: Marzano, 2004, p. 32.
To interpret the correlations in table 1.2, keep in mind that a perfect positive relationship between two variables is indicated by a correlation of 1.00. As one variable increases, so does the other. Therefore, correlations approaching 1.00 (such as those shown in table 1.2) are considered quite strong.
There are several possible reasons for the correlation between vocabulary and intelligence. First, Stahl (1999) suggested that students who have higher general ability (or intelligence) are simply better at more things, including learning new vocabulary words. Alternatively, Sternberg (1987) postulated that students with higher intelligence learn better from context, and so soak up more words as they encounter various situations. However, it is also possible that students with larger vocabularies can understand more information and therefore analyze information more effectively, thus allowing them to perform better on intelligence tests. A study by Brent Berlin and Paul Kay (1999) illustrates this principle. Berlin and Kay investigated different cultures’ perceptions of color. They discovered that some cultures had fewer terms for colors than others. For example, some cultures only had color terms for light and dark; others for light, dark, and red; others for light, dark, red, and green; and
