O.F.T. (Outstanding for Trolls) is a grade that a troll would achieve if it managed to use a computer and take the W.O.M.B.A.T. test.
The W.O.M.B.A.T test was published on J.K. Rowling's original website, which has since been taken down.
W.O.M.B.A.T stands for Wizards' Ordinary Magic and Basic Aptitude Test. It's administered by the Wizarding Examinations Authority. The head of this Authority is Griselda Marchbanks, CDMG, APMD, fbBB.
The W.O.M.B.A.T. test Grade 1 first appeared on Rowling's website on March 31, 2006.
W.O.M.B.A.T. test Grade 2 appeared on September 29, 2006.
The W.O.M.B.A.T. test Grade 3 appeared on June 14, 2007.