Are your pupils getting enough sleep? The latest research suggests it is unlikely. Recent NHS data revealed that the number of under-14s being assessed in hospital for sleep disorders had tripled in 10 years.

Some sleep scientists are also convinced that the school day should start later to accommodate the shifting circadian rhythms that make it difficult for teenagers to get up early. And Professor Matthew Walker, a neuroscientist at the University of California, Berkeley, and author of the international bestseller Why We Sleep: the new science of sleep and dreams, has called for government involvement in helping families to get to bed on time.

The impact of these sleep problems is not simply tired children. A growing body of evidence is unpicking the role that sleep plays in learning and memory consolidation - in other words, why getting some shut-eye is vital for academic achievement.

For example, in an ongoing study funded by the Economic and Social Research Council at the Sleep, Learning and Memory Lab based at Royal Holloway, University of London, researchers are investigating how sleep deprivation in adults affects their ability to recall a new script (made-up words comprising made-up letters). Participants learn a new script, then stay awake all night. Even after a couple of nights of subsequent recovery sleep, there’s a difference in how quickly they can recall words compared with a control group that doesn’t experience sleep deprivation.

Similarly, in a 2014 study from the UCL Institute of Education by Ashworth et al, in which six- to 12-year-olds were taught novel (or “made-up” ) words for animals, there was a 14 per cent improvement in recall after a period of sleep compared with time spent awake.

You snooze, you win

Dr Anna Weighall, a cognitive developmental psychologist based at the University of Sheffield, is one of the key researchers in this field, and she says that a clearer picture is emerging of how important sleep may be to the learning process.

“Sleep isn’t just about making children feel better during the day; it’s integral to the way in which their memories work,” she explains. “As well as [children] needing to be alert in order to process information in the first place so that it can be stored, sleep plays an active role in the way that children’s memories work with information learned during the day.

“We need to think of memory as being really fragile. When you learn something, you’re at risk of forgetting it, thanks to all the other conflicting information that’s coming in. So we think sleep protects against that.”

It seems children have an edge over adults in the sense that, until around the age of 12, they experience more slow-wave sleep (SWS). This is a non-rapid eye movement (REM) phase of deep sleep that plays an important role in forming and retaining memories. During SWS, the hippocampus - which is where new information is initially stored - is in communication with the neocortex, where that information is strengthened, cemented and filed for long-term memory.

Weighall and University of York colleagues Professor Gareth Gaskell and Dr Lisa Henderson claim to be the first to have uncovered evidence of a link between sleep and vocabulary acquisition in children.

In one study, they recruited 53 children aged 7 to 12 from three boarding schools in North Yorkshire. Children learned 16 “novel” words - made-up words that sound similar to existing words - either in the morning or early evening. They were tested on recall immediately afterwards, 12 hours later, 24 hours later and one week later.

“We showed that children’s ability to recognise and recall novel non-words was associated with sleep,” says Weighall. “Children accurately recognised new words immediately after exposure, but significant improvements were shown after 12 hours only for the [group who learned words in the early evening] who had slept. For the students who learned in the morning, we saw significant improvements after 24 hours - that is, after they had slept.”

An element of lexical competition was also uncovered. “As well as measuring whether children could recall the words they had learned, we also looked at whether they could integrate them with existing knowledge,” Weighall explains. “When does a new word start to behave like a ‘real’ word that you know already?

“What we know about the way the mental dictionary works is that, when you hear a word in speech, your brain starts to try and predict that word as quickly as possible - we almost try to ‘guess’ what the word will be. For words that have few similar-sounding neighbours - ‘banana’, for instance - that’s easy. But some words have lots of competitors that sound similar: ‘beach’, ‘bees’, ‘beats’, ‘beef’, ‘peach’, ‘teach’. In this case, the words in the mind compete or race for recognition. This means that it is quicker and easier to recognise a word that doesn’t have so many neighbours.

“If we teach children a new word that competes with a word already known - for instance, ‘biscal’ overlaps with ‘biscuit’ - it will slow down recognition of the word ‘biscuit’ because now there are more competitors. This process is called lexicalisation, and we found that learning ‘biscal’ does indeed slow down how quickly children (and adults) recognise ‘biscuit’, but only after sleep.

“This suggests that sleep is really important for consolidating new learning and that it has an active role to play in enabling our brains to integrate new knowledge into our existing memory.”

While Weighall’s research focuses on sleep and vocabulary acquisition, similar findings are replicated across other areas of learning - for example, research by Dr Ines Wilhelm, from the University of Zurich, shows that, after a period of sleep, children perform better on a motor sequence task than adults.

All this is very important background information for teaching, but educators have no control over how much sleep their pupils will get. However, Weighall believes that, while teachers are not directly responsible for their students’ sleep routines, they can open up a dialogue about them in the classroom.

“When I speak to teachers in schools where I conduct research, they’re always worried about children being tired. And rightly so,” she says. “Children have got so much going on when they get home from school - activities, social media, homework - and they need time for peace and quiet, to consolidate the learning that’s happened during the day. In much the same way that teachers might talk to their students about exercise and eating well, they can have conversations about prioritising sleep.

“If [pupils] have got tests coming up, I think it’s crucial that teachers are advising against revising at the expense of sleep, because research shows it’s counterproductive. Partly because cramming isn’t good for memory and also, if you’re having less sleep, you’ve got less opportunity for consolidation to take place.”

Lighten the cognitive load

Weighall also believes that there are lessons from her research that teachers can build into the classroom environment.

“As well as memory consolidation during sleep, there is some research to suggest that, when we’re learning, if you have a little bit of quiet time afterwards, this can also support memory. Teachers can think about the way in which they structure the school day, by building in time for reflection and not doing too much of the same activity all at once, so the children have time to lay down those memories.

“Lack of sleep can be thought of as taxing, or reducing, cognitive resources. If a child is tired, they will have less cognitive resources available [so] their ability to cope with high cognitive load may be reduced, meaning that classroom techniques that reduce unnecessary cognitive load are likely to help all children, but they may be particularly beneficial for those who are tired. Interestingly, poor sleep and tiredness can result in children having reduced attention spans and, in severe cases, can even lead to behaviour that can look very much like ADHD [attention deficit hyperactivity disorder].”

Weighall is now interested in how other states, such as exercise, might boost learning and how this could be used to structure the school day. But for now, her message is clear: for children to have the best chance of learning success, a good night’s rest is non-negotiable.

Christina Quaine is a freelance journalist

Meet the academic

Dr Anna Weighall is reader in education and director of MSc psychology and education at the University of Sheffield. She is a cognitive developmental psychologist whose research specialism is sleep, memory, language learning and cognitive development in children and adults. She is also interested in how interventions to improve physical and mental health and wellbeing can improve cognitive and educational outcomes for children and their families.

References

Ashworth, A, Hill, C M, Karmiloff-Smith, A, et al (2014) “Sleep enhances memory consolidation in children”, Journal of Sleep Research, 23: 304-10, bit.ly/SleepyMem

Henderson, L M, Weighall, A R, Brown, H, et al (2012) “Consolidation of vocabulary is associated with sleep in children”, Developmental Science, 15/5: 674-87, bit.ly/VocabSleep

Wilhelm, I, Rose, M, Imhof K I, et al (2013) “The sleeping child outplays the adult’s capacity to convert implicit into explicit knowledge”, Nature Neuroscience, 16: 391-93, bit.ly/SleepKnow

Further reading

Walker, M (2017) Why We Sleep: the new science of sleep and dreams by Matthew Walker (Allen Lane)

”How much sleep do children need?” (NHS, bit.ly/NHSsleep)

Gregory, A (2018) Nodding Off: the science of sleep from cradle to grave (Bloomsbury)