Young children whose parents read them five books a day enter kindergarten having heard about 1.4 million more words than kids who were never read to, a study has found.
This "million word gap" could be one key in explaining differences in vocabulary and reading development, said Jessica Logan, assistant professor at The Ohio State University in the US.
Even kids who are read only one book a day will hear about 290,000 more words by age 5 than those who don't regularly read books with a parent or caregiver.
"Kids who hear more vocabulary words are going to be better prepared to see those words in print when they enter school," said Logan, lead author of the study published in the Journal of Developmental and Behavioral Pediatrics.
"They are likely to pick up reading skills more quickly and easily," Logan said in a statement.
Logan said the idea for this research came from one of her earlier studies, which found that about one-fourth of children in a national sample were never read to and another fourth were seldom read to (once or twice weekly).
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"The fact that we had so many parents who said they never or seldom read to their kids was pretty shocking to us. We wanted to figure out what that might mean for their kids," Logan said.
The researchers identified the 100 most circulated books for both board books (targeting infants and toddlers) and picture books (targeting preschoolers).
They randomly selected 30 books from both lists and counted how many words were in each book. They found that board books contained an average of 140 words, while picture books contained an average of 228 words.
With that information, the researchers calculated how many words a child would hear from birth through his or her 5th birthday at different levels of reading.
They assumed that kids would be read board books through their 3rd birthday and picture books the next two years, and that every reading session (except for one category) would include one book.
They also assumed that parents who reported never reading to their kids actually read one book to their children every other month.
Based on these calculations, kids who have never been read to would have heard 4,662 words by the time they were 5 years old. Those who are read five books a day, hear about 1,483,300 words.
"The word gap of more than 1 million words between children raised in a literacy-rich environment and those who were never read to is striking," Logan said.
"This isn't about everyday communication. The words kids hear in books are going to be much more complex, difficult words than they hear just talking to their parents and others in the home," she said.
For instance, a children's book may be about penguins in Antarctica -- introducing words and concepts that are unlikely to come up in everyday conversation.
"The words kids hear from books may have special importance in learning to read," Logan said.