The OECD released last month the 2009 PISA results. These tests assess the achievement of 15-year-olds along reading, maths and science, and are regarded by many as a key tool to monitor the quality of each country's education system.
The results for Portugal indicated a very sizable improvement, when compared to 2006 and earlier results (link). For instance, the reading score increased from 472 to 489, placing Portugal at the OECD mean - and above countries such as Spain, the Czech Republic, Slovakia or Austria. The government hailed these findings as vindication for all the reforms introduced since 2005; while many teacher blogs (link) raised questions about the validity of the results. These questions became more vocal when the education ministry refused to release the list of presumably randomly-selected schools in the survey (link).
As someone that has studied the effects of one of the reforms introduced by the former government - the new teachers' assessment and incentives structure -, I too am curious about the validity of these 2009 PISA results for Portugal. Especially, as I found evidence that those teacher reforms had a detrimental effect on student achievement (link). So to shed some light on this issue I analysed the PISA micro data (available from here) from 2006 and 2009 but splitting the weighted results between public and private schools and not simply looking at their mean.
In the case of reading, this is what I found:
First, perhaps unsurprisingly, the results indicate that students in private schools appear to do better than students in public schools, both in 2006 and 2009. Second - and more important -, the gap between private and public schools remains virtually the same over the three-year period.
The results are very similar for sciences and maths:
According to my previous research, I actually expected the public-private gap to widen. On the other hand, it's difficult to reconcile the government view that the improvement in Portugal's PISA results was due to its reforms with the fact that private schools see their PISA scores increase by a similar level than public schools. For instance, and as far as I know, the teachers' assessment structure in private schools was not subject to the same adjustments as in public schools.
If one looks at the case of Spain, the pattern there is much more mixed - improvements in reading, as in Portugal, but stable results in sciences and maths, at both public and private schools:
To wrap up, I am not sure what explains this massive improvement in the perceived achievement of Portuguese students in the two types of schools. Some hypothesis are:
-successful reforms implemented by the government matched by equally successful reforms implemented by private schools, even if in a more decentralised manner;
-composition changes between private and public schools, in such way that both means improve over time;
-more generous marking.
It would be really important to clarify this - otherwise we can end up vindicating the wrong policies - or not vindicating the right ones...