Children who demand the same story to be read to them over and over again may be learning more than those who get a different story every time. 

New research at Sussex shows that repetition in reading storybooks is more likely to lead to a child acquiring new vocabulary - even if it sends the parents off to sleep. 

Psychologist Dr Jessica Horst and her team devised an experiment in which three-year-olds were exposed to two new words.  Each word was a made-up name for an unfamiliar object (for example, a 'sprock', which was a hand-held device used for mixing food). Over the course of one week, one group heard three different stories with the same new words. Another group heard only one of the stories with the same new words.  Each book contained drawings of the new objects. 

When tested after a week, those who had heard just one story were much better at recalling and remembering the new words than those who had been exposed to three different stories. 

Dr Horst says: "We know that the more books you have at home, the higher the academic achievement of children.  But what we haven't understood is actually how that learning happens. 

"This research suggests that it's not the number of books, but the repetition of each book that leads to greater learning.  We know that children who watch the same TV programme over and over again do better in comprehension tests afterwards. What we think is happening with reading is that each time a child hears the book they are picking up new information. The first time it might just be the story, the second time they are noticing details of description, and so on. If the new word is introduced in a variety of contexts - as happened with those who were read three different stories - children are less likely to focus on the new word." 

She adds: "I think the message here could be that children don't necessarily need a vast quantity of books, but they do benefit from repeated exposure to those books." 

'Get the story straight: contextual repetition promotes word learning from storybooks', by Jessica S Horst, Kelly L Parsons and Natasha M Bryan, is published in Frontiers in Psychology, February 2011.