The other day I had a random thought about about a corner of the rules I hadn't considered before, and I'm curious if other people will come to the same conclusion as me. The question is whether or not a Wizard who prepares a spell from an opposed school (which uses two spell slots) could use a Pearl of Power normally to restore the spell once cast. I can see room for an argument that you would need TWO Pearls of Power to recall a spell that took two slots to prepare in the first place, but I don't think that's actually the correct conclusion.
Looking at the text of Pearls of Power,
"This seemingly normal pearl of average size and luster is a potent aid to all spellcasters who prepare spells (clerics, druids, rangers, paladins, and wizards). Once per day on command, a pearl of power enables the possessor to recall any one spell that she had prepared and then cast that day. The spell is then prepared again, just as if it had not been cast. The spell must be of a particular level, depending on the pearl. Different pearls exist for recalling one spell per day of each level from 1st through 9th and for the recall of two spells per day (each of a different level, 6th or lower)."
I see no mention or reference to spell slots; a Pearl of Power allows a prepared caster to recall one spell. Because a spell from an opposed school is still just one spell (even if it does take up two slots), I think a single Pearl of Power of the appropriate level is sufficient for allowing a Wizard to recall a prepared spell from an opposed school. Is this just obviously the right answer, or is there anyone out there who would disagree?
Sounds like it works. There is no restriction on opposition school spells, and it makes no mention of the number of slots the spell takes up. I could see a GM ruling otherwise, but I don't see any problems with the straightforward interpretation here that it restores a spell irrespective of how many slots that spell took.