Global Education Indicators - dataset
You can use the PISA study from OECD. It evaluates the skills and knowledge in reading, mathematics and sciene of 15-year-old students. PISA does not combine these results, but commentators do so sometimes.  

The most recent results are from 2012, you can find an overview of the rankings here. These rankings are composited from various tabels you can download using the links at page 297 from this document.
Results of 2009 are available in a xls-file. Scroll down this artcile to download.