There is often talk on here that people think that primary school results are inflated. It might not be as common as 'reported' as it would appears, as a school in Wales has just been placed in special measures after ESTYN inspection because of it (along with other concerns)...
"Across the school, the work seen in books and lessons during the inspection does not consistently match end of key stage teacher assessments. In most cases, pupils are working at a much lower level."
news report here