Anybody judging a large number of anythings, whether they are marrows or lessons will pre decide an average grade (ie satisfactory) as you look a bit silly if you always judge things to be 'excellent' or 'rubbish'.
The worst case conclusion from these results is that half of lessons are better than average and half are worse. Well I'd never have worked that one out. What a great use of public money.
I'll go through Ofsted's criteria for judging lessons in the near future (and if you're the parent of a bright kid, you will be horrified).