There can't be a parent around who has not warned their youngsters they'll suffer at school the next day if they don't get to sleep THIS minute - and now the scientific proof is here to back us up!
A study was carried out on 142 primary school age pupils by the Autonomous University of Barcelona, and its findings back up what parents have been saying for generations, that sleep- deprived kids are not on the ball in lesson time.
The research came about as experts express fears over the amount of time kids spend in their bedrooms on computers and gaming.
Ramon Cladellas, the study's lead researcher, said a good night's sleep was of huge importance to growing youngsters.
He said: 'Most children sleep less than is recommended for their intellectual development, which is hindered because the lack of sleep cannot be recovered.
'Pupils that sleep eight or nine hours have a worse performance than those that sleep nine or 11 hours.
'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.'
During the study, the researchers compared the amount of sleep the youngsters got with their performance in a range of academic skills.
Most six and seven-year-olds who had not had enough shut-eye were found to be less able to communicate and work out basic maths questions, whilst their spelling, grammar and comprehension went downhill.
Despite this, their memory and ability to learn were not particularly affected - but this is the bit we don't tell the kids!
Are you strict and rigid with bedtimes for your children?
Can you see a huge difference in their concentration and behaviour if they are tired?