A total of 188 out of 745 children surveyed said they normally carried bags weighing an average of five kilos (11lb 1oz) - the equivalent of 14% of their body weight.
And the people who carried out the survey are calling on schools to make pupils keep their bags in lockers and give them more time to move from one lesson to the next.
The research warns that heavy loads increas the risk of back injury and permanent changes to the way you normally stand.
On the plus side, fewer than 1% of the parents surveyed had ever examined the contents of their kids' schoolbags!
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