The theory was first described in England back in 2011 when objectively measured activity (via accelerometers) from children attending 3 schools with widely varying amounts of prescribed PE, was shown to be roughly equivalent.
Well a few weeks ago, these findings were confirmed in Denmark where researchers compared the objectively measured activity of children in "sport schools" and regular schools. The sport schools provided children with a minimum of 4.5 hours of activity weekly, while the regular schools saw their kids moving weekly for 1.5 hours - and yet all kids, regardless of school, accumulated roughly the same amount of weekly activity.
Me? I'm all for well designed PE classes to help children both develop and accumulate physical literacy and to improve their school based attention and behaviour. I'm also all for increasing recess duration and frequency and lifting school yard safety restrictions. But if you think that simply adding more PE to school is going to have a tremendous impact on getting kids these days to be more active (or lose weight), there's a growing body of evidence that suggests that it won't.