Unless he's going to let you put skill points into initiative it isn't a skill.
Please note it doesn't affect strength and dexterity checks, only skill checks.
My GM is reading the core rule book verbiage "APC affects all strength and Dex based skill checks"
Initiative is a Dex check but he believes that APC applies to it. Is this called out by a Paizo person or errata anywhere?
Initiative is not a skill check. It is more accurately an Ability Check. Armor Penalty Checks do not apply to Ability Checks, only to skill checks.
Got any errata or Paizo posts to back this? That's pretty much all he'll accept.
No errata necessary:
PRD:
Armor Check Penalty: Any armor heavier than leather, as well as any shield, hurts a character's ability to use Dexterity- and Strength-based skills. An armor check penalty applies to all Dexterity- and Strength-based skill checks. A character's encumbrance may also incur an armor check penalty.
PRD:
At the start of a battle, each combatant makes an initiative check. An initiative check is a Dexterity check. Each character applies his or her Dexterity modifier to the roll, as well as other modifiers from feats, spells, and other effects. Characters act in order, counting down from the highest result to the lowest. In every round that follows, the characters act in the same order (unless a character takes an action that results in his or her initiative changing; see Special Initiative Actions).
Initiative checks are not skill checks. They are ability checks.
