School Savant and Opposition School preparations

[Snow_Tiger]

it says
"Finally, the arcanist must select two additional schools of magic as her opposition schools. Whenever she prepares spells from one of her opposition schools, the spell takes up two of her prepared spell slots. In addition, a school savant takes a –4 penalty on any skill checks when crafting a magic item that has a spell from one of her opposition schools as a prerequisite. A school savant cannot select the school understanding arcanist exploit. This ability replaces the arcanist exploits gained at 1st, 3rd, and 7th levels."

by "two of her prepared spell slots" does this mean the arcanist prepares at twice cost and casts at 2 spell slots? a little confused on wording

[OmniMage]

I think its written clear enough. It basically mimics the specialist wizard.

A single prepared spell of an opposition school would occupy 2 spell slots. You would only get 1 spell for the price of 2. This means its more expensive to cast an opposition school spells. A specialist wizard is not very good at casting spells of an opposition school, hence why they waste a whole spell slot.

Back in DND 3.5, a wizard could not cast any spells of an opposition school, so wasting spell slots in Pathfinder can be seen as an improvement.

There is an arcane discovery that eliminates this problem. Opposition Research. I would rule that an Arcanist, school savant archetype, may pick this if they could not already. You would need to pick it twice to eliminate of all opposition schools.
https://www.aonprd.com/WizardArcaneDiscoveries.aspx

[Lelomenia]

I don’t see an indication that it would use two casting slots to cast, just two prepared spell slots to prepare. That said, the word ‘slots’ is reserved in arcanist etc descriptions for a characters daily use cast consumable, so the word choice is bad.

[OmniMage]

I might have not been clear enough earlier. Opposition schools require 2 slots to prepare, 1 slot to cast.