A connection between sleep and learning has already been identified as beneficial for adults and older children.
Now University of Sussex psychologists Dr Jessica Horst and PhD candidate Sophie Williams have shown that three-year-olds who take a nap after having stories read to them will also perform better later in word-learning tasks.
Their study, published in Frontiers in Developmental Psychology today, involved 48 British children, half of whom took afternoon naps, and half of whom didn't.
They were read either the same story, or three different stories, but were exposed to the same number of unfamiliar words.
When tested two and a half hours later, 24 hours later and a week later, those children who had been read the same story before their nap performed significantly better than those who hadn't had a sleep.
Significantly, those children who had been read three different stories before their sleep performed 33 per cent better than those who had stayed awake after hearing those stories.
On subsequent tests, the researchers found the wakeful ones never caught up with their peers in word recall.
But the new study shows that sleep can have an additional significant advantage, especially when the children are exposed to different stories.
Dr Horst says: "Overall, all of the children in the study did very well—reading is always good, at any age and any time.
But, children who were learning something particularly difficult (new words from several stories) especially benefited from hearing the stories right before sleeping.
In fact, these children ended up learning the words as well as the children who had heard the same stories again and again, which we knew would be easier."
Dr Horst points that many studies have shown young children are now sleeping less than ever before and consistently less than recommended guidelines.
Chronically short sleep is significantly related to poorer vocabulary scores, childhood obesity and externalising behaviours, such as tantrums.
"Many preschool children take an afternoon nap, yet classroom naps are increasingly being curtailed and replaced due to curriculum demands," she adds.
"Given the growing body of evidence that sleep consolidation has a significant effect on children's learning, such policies may be doing our children a huge disservice."
"In fact, findings like those from the current study indicate we should be encouraging young children to nap and should take advantage of the period right before they nap for instruction in key academic areas such as word learning and arithmetic."
More information: "Goodnight Book: Sleep Consolidation Improves Word Learning via Storybooks." Sophie E. Williams and Jessica S. Horst. Front. Psychol. DOI: 10.3389/fpsyg.2014.00184