They then spent over an hour revising Summoning Charms, which according to Professor Flitwick were bound to come up in their O.W.L. (OP13)
while teachers were firing revision questions at the class (OP28)
Hermione, as was her custom, had spent a large part of the day drawing up revision timetables for the three of them (OP29)
Reviewing work already learned or done, especially to prepare for an examination (NSOED).