Taking the 'P' Out of PISA?

It's that time of the year again (shortly after 'manic Monday') when the Pisa 'comparisons' between school systems in many (but far from all) of the world's countries are made on the basis of testing samples of selected students in mathematics, reading and science (http://www.bbc.co.uk/news/education-25090033 ). In fairness, even the people who run the tests point out some of the problems (e.g. some languages are more phonetic than others, some countries show big geographical diversities in attainment, different levels of extra-curricular coaching is evident in some groups, happiness doesn't always equate with success in the tests, many subjects are not tested, the tests don't attempt to measure creativity etc, etc). Yet everytime these tables are published, the media and politicians of all stripes go bananas. The power of a table!