Data is freely available from the World Bank DataBank website.
Browse or search the Data Catalog which provides access to 2,000 indicators
You can also link directly to the Data Catalog Education Statistics page or with the increase of freely available datasets read the British Educational Research Association's paper on using large scale datasets in research.
Explore the World Bank's open data initiative.
OECD iLibrary is the online library of the Organisation for Economic Cooperation and Development.
Featuring its books, papers and statistics and is the gateway to OECD’s analysis and data in OECD.Stat (see more about OECD.Stat in box below). You can browse by theme (e.g. education) and country/countries and it also contains content published by PISA (Programme for International Student Assessment).
Getting started Quick Guide for the for OECD iLibrary
OECD.Stat User Guide (PDF 40 pages)