I think this is too expensive, and I think the "initiate" rules in Swordsman's Guild did it the wrong way around.
costs 20 XP, sets mastery at 0, and grants the ability to use the apprentice ability of the school, as well as any Swordsman knacks in the school you have from other schools. If you have a similar apprentice ability the price is reduced to 15 XP
Onwards to Apprentice
Every swordsman knack costs 5XP once you have them all you are an apprentice. Exploit Weakness gains a 1XP discount for every tick the char has in the relevant Knowledge i.e. it you have full knowledge of the school you get EW (SS) for free.