This paragraph tells you most of what you need to know:
The Scottish Government wants all primary schools to offer two hours of physical activity for all children each week - but figures from 2005 show that 5% of primary schools were meeting the provision.
I suppose the situation may be better in secondary schools but to the extent that childhood obesity is a problem, you're likely to have more success exercising the brutes than trying to monitor and control the sort of junk with which they stuff their faces. Plus, there are other benefits from sport too. But no, it's more sensible to sell off the playing fields...