Primary school pupils need to have at least nine hours' sleep each night or their capacity to learn will be impaired, say researchers.
The research carried out by the Autonomous University of Barcelona examined the link between sleep and children's intellectual development.
It found that a lack of sleep damaged core skills needed for learning.
The researchers suggest parents should be taught about the importance of sleep for their children's well-being.
The study found that even those children who had eight to nine hours of sleep were more likely to struggle in school compared with children who slept for nine to eleven hours.
This threshold of nine hours as a minimum was based on an examination of the sleeping patterns of 142 six to seven year olds in a range of schools in Spain.
The study found that "memory, learning and motivation" were all disrupted by insufficient sleep or the lack of a regular bedtime routine.
There were also specific problems associated with a lack of sleep, such as in language and writing.
"The lacking hours of sleep distorts children's performance in linguistic knowledge, grammar and spelling rules, and key aspects in the organisation and comprehension of texts, to name a few examples," said Ramon Cladellas, a researcher from the university's psychology faculty.
"They are basic skills, meaning that if the pupil, due to a lack of sleep, develops problems in this area, it could have a repercussion on all subjects."
Mr Cladellas said that parents needed to be made aware of the significance of making sure their children got enough sleep.
"Nowadays, there is great concern because children are glued to the television, computers, and video games, but the same importance is not given to them going to bed at the same time every night."
This is the latest study to make a connection between children's sleep and their capacity to learn and their behaviour in school.
Research from the University of Michigan in the United States, published during the summer, found that school bullies and aggressive pupils were much more likely to be the pupils who did not get enough sleep or who were suffering from sleep disorders.
It suggested that over-tired pupils did not have the "emotional regulation necessary to control aggression".
A previous study of seven and eight year olds in Finland found that the behaviour of sleep-deprived children had many similarities with the behaviour associated with ADHD (attention deficit hyperactivity disorder).
It found that children who slept less than eight hours were the most likely to show this disruptive behaviour.