Sweden was the original inspiration for the Conservatives' free schools. But now, as the Tories plan to step up the pace, that country is plunging down the league table of learning

The concept of evidence is not, it seems, on the curriculum at the top-notch schools that educate Britain's leaders. George Osborne cut the 50% top tax rate before it had bedded in, so that the data was still distorted by wealthy people paying themselves early to avoid its effect. The bedroom tax, a government-commissioned analysis found last year, is failing in its purported purpose of encouraging tenants to move out of unnecessarily large homes: fewer than one in 20 has done so. No matter, the policy rolls on.

Then there is schooling, where Michael Gove's wholesale revolution in governance was rushed through without considering the questions of those awkward sorts that the Bush White House used to dismiss as "reality-based communities" – questions about whether the stampede to open free schools and confer academy status would make things better or worse. Now, however, the OECD – the rich-country club which can hardly be dismissed as part of the educational "blob" that Mr Gove used to set himself against – brings worrying news about the country that the former education secretary used to describe as his inspiration.

Sweden, a frequently-used but frequently misleading byword for a social democratic nirvana, began experimenting with publicly funded "independent" schools over 20 years ago. Over time nagging doubts grew about whether these islands of educational autonomy were working to increase segregation, both between the social classes and between immigrants and nationals. Steadily, however, they became entrenched as part of the system and were for the most part accepted as a useful bit of grit in the oyster when it came to raising average standards. Not any more, however.

Reviewing the best comparative evidence, the OECD describes "a decade of declining ... performance". Scores for reading, maths and science are all on the slide, and overall the Nordic state has declined from "around average" to "significantly below average" in the global league table of learning, a bigger drop than any other country has seen. Of course many things besides the Swedish version of the free schools programme have been going on during these years, including immigration and a widening of Sweden's traditionally narrow income gap. It would be foolish to pretend that everything can be blamed on the shift to "contestable" educational provision. But it would be equally rash to brush off this cautionary tale, which, at the least, suggests that creating hundreds of independent institutions offers scant protection against a slide in standards.

The OECD suggests that increasing the attractiveness of the teaching profession, improving pedagogical leadership and investing in professional development might be more fruitful avenues to pursue. The Conservative manifesto, however, does not propose to see how the first 250 free schools already created turn out. Instead, at a time of rising demographic and financial pressures, it commits to create 500 more. Open minds and patient study are two preconditions of successful learning. Both would appear to be in short supply in today's Tory party.