?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.au=Wiliam%2C+Dylan&rft.aufirst=Dylan&rft.aulast=Wiliam&rft.pages=279-239&rft.atitle=It%E2%80%99s+not+which+school+but+which+set+you%E2%80%99re+in+that+matters%3A+the+influence+of+ability-grouping+practices+on+student+progress+in+mathematics&rft.title=British+Educational+Research+Journal&rft.volume=30&rft.date=2004&rft.issue=2&rft.issn=1469-3518&rft.genre=article