Putting children to bed at the same time every night could help boost their brain power, researchers have found.
A study of more than 10,000 youngsters revealed their cognitive development is affected by inconsistent bedtimes.
Authors of the report tested children's abilities to perform certain tasks by testing their reading, math and spatial awareness.
They found that 3-year-olds who went to bed at irregular times performed worse than those who were put to bed at the same time throughout the week.
The effect was also seen in 7-year-old girls, although boys were not affected. There was no link in girls or boys at the age of 5.
"Sleep has a crucial and complex role in the maintenance of health and optimal function," the authors wrote in the Journal of Epidemiology and Community Health.
"Inconsistent bedtime schedules might impact on markers of cognitive development in two ways, via disruptions to circadian rhythms (physical, mental and behavioral changes) and/or sleep deprivation and associated effects on brain plasticity (the brain's ability to change during life)."
Laura Downes, a special needs primary school teacher from Ealing, west London, has a well-drilled routine in place for her 3-year-old daughter Elizabeth.
She told Sky News: "The routine is key. It needs to be rigid and the same. For us, this means a fail-safe tool to fall back on.
"Whatever happens during the day or whatever is going on ... she knows that routine is coming up."