Time allocated for PE has been squeezed and teachers' increased workload means they no longer have the time or inclination to run after-school games.
"Added to this has been the very understandable reluctance of schools and teachers to encourage any activity that might be seen as risky, and therefore make them liable to litigation," he says.
Prince Philip's comments came as he gave his support to the TES Get Active campaign, which is designed to help schools tackle the worrying rise in child obesity.
He has strong links to the world of sport as president of the Central Council for Physical Recreation, a group including sports governing bodies and teaching unions. His Duke of Edinburgh award scheme has 225,000 young people taking part in outdoor activities.
Prince Philip's comments follow concerns raised by David Bell, the chief inspector of schools, who asked last month whether it is "time to inject more of the physical into physical education?".
A Department for Education and Skills survey last week showed that only a third of five and six-year-olds are meeting the Government's target and doing two hours high-quality PE and school sport each week.
But the Duke of Edinburgh says in The TES: "My impression is that the pendulum is beginning to swing back towards those who would like to see better PE provision and a greater emphasis on the value of regular exercise for every age-group in the community."
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