A survey of 250 primary school teachers showed nine out of 10 believe pupils are too tired to pay attention. Nearly a quarter of teachers let children sleep in a corner of the classroom.
More than a third said lack of sleep was a daily problem, most blaming TVs and computers in bedrooms and parents being too lax about bed times.
The Sleep Council's poll revealed that a lack of sleep among primary school children is having a devastating effect in schools with nine out of 10 teachers complaining that pupils are so tired they are unable to pay attention in class.
More than a third said lack of sleep among youngsters is a daily problem for them.
Nearly nine out of 10 teachers felt that too many distractions in the bedroom (like games consoles and TVs) were at the root of the sleep related problems along with the fact parents are simply not strict enough about enforcing bedtimes.
More than half of those questioned agreed that the brightest children in the classroom are the best slept and most wide awake.
The Sleep Council is launching its first ever "sleep awareness" project in schools – "Better Brains with More Sleep" – as part of March's National Bed Month.
It aims to teach primary school children the importance of a good night's sleep and the factors – such as regular bedtimes and a good bed – that can affect it.
"As part of our project we wanted to establish just how much of an issue lack of sleep has become among young school children," said Jessica Alexander of The Sleep Council.
"Even we have been taken aback by the sheer scale of the problem."
Lack of sleep has now become so widespread in primary schools that nearly a quarter of the teachers questioned admitted that they had had to resort to letting children who are very tired sleep in a corner of the classroom."
Siôn Humphreys, Policy Advisor for the National Association of Headteachers, said: "NAHT is pleased to support this important initiative, drawing attention as it does to an oft-hidden yet significant matter.
"Schools cannot succeed without effective partnerships with the home. A tired and irritable child will not thrive, particularly in the active and pacey modern classroom.
"NAHT is particularly concerned about the still small but rising numbers of pupils who stay up late engaged in online gaming."
• The Sleep Council's free 'Good-Night Guide for Children' booklet is filled with hints and tips for parents on how to help their children get a good night's sleep. It can be downloaded from www.sleepcouncil.org.uk or requested by calling the leaflet line on 0800 018 7923.