Reading and vocabulary growth are closely intertwined. The better a child's vocabulary, the better she understands what she reads. The more a child reads, the faster his vocabulary grows. Together, these observations have led to another, known as the "Matthew effect." Coined by a reading researcher, Keith Stanovich, the term "Matthew effect" refers to a point in the Gospel of Matthew which says that the rich get richer and the poor get poorer. In reading, strong readers become ever stronger, while poor readers fall further and further behind.
How does the Matthew effect come about? Struggling readers, those who are having difficulty sounding out or figuring out words, are exposed to less text every day in school. They read simpler books, and they read slowly, laboriously working their way through the sentences. Moreover, they are far less likely than fluent readers to read outside of school. Why would they choose to do something that is so hard and frustrating?
By fourth grade, according to Anderson and Nagy, the difference in reading volume is huge. The average fourth grader (the child at the 50th percentile) spends 14 minutes a day outside of school reading any kind of text. That adds up to reading about 600,000 words a year. The child at the 90th percentile reads 54 minutes a day, or 2.36 million words a year, almost four times as many. Meanwhile, the child at the tenth percentile reads on average only about a minute a day, for a mere 51,000 words a year. Between the 10th and 90th percentile, that's a huge, 50-fold difference in exposure to written words.
The difference matters, because kids who read more gain more knowledge of vocabulary and more background knowledge. The more they read, the more they understand. It's easier for them to learn new material because they have a context which that new material can fit into. They understand pyramids in math because they've read about pyramids in ancient Egypt; they can learn about American history because they aren't scared off by such words as assembly, representation, and compact.
In their research on vocabulary development, Anderson and Nagy look back to early child development in the home. By now it's common wisdom that well-off parents talk to their children more than do parents in poverty or on welfare. In an average hour, working class parents say twice as many words to their children as do welfare parents; professional parents say almost twice as many again. Moreover, the balance of communication among welfare parents is much more tipped toward telling kids what they may not do: 11 prohibitions and 5 affirmations per hour in welfare families, versus 32 affirmations and only 5 prohibitions per hour in professional class families.
The result of this difference in conversational exposure means that children of professionals come to kindergarten knowing on average more than 3 times as many words as children from welfare families.
What does this mean for parents? It means it's important to talk to your young children and to include them in family conversation as much as possible. It also means that older children can still benefit from being read to. If you have a child who dislikes reading and resists picking up a book, it's important, at the same time as you're working to address the reading difficulty, to keep exposing the child to rich vocabulary and rich ideas through reading aloud. Surprising as it may seem, research shows that even a pre-school picture book is richer in unusual words, those that will stretch a child's vocabulary, than is prime time television or the conversation of college graduates with their family and friends.