Concentration Check question.....

[4saken1]

Say a spellcaster moves or performs a movement action before casting a spell, provoking an attack of opportunity - Do they still need to make a Concentration Check if they are hit before they even end their movement and begin casting?

[snotling]

Attacks of Opportunity and such are not part of the BB - so from the BB point of view, no.

Depending on how your DM uses AoO. Here is how I play it:

A successful AoO as an interruption to the action, and ends the players turn (after the action is completed). In this case, the character will move provoking the AoO. The AoO is taken and a success happens. The player is stabbed when moving. The player finishes the move action but the turn is now over as the AoO interrupted the normal flow of actions.

[Sean K Reynolds]

AOOs don't interrupt actions unless the action says it does.

So if you move (and provoke an AOO), that doesn't block your move.
And if you had planned to cast at the end of your move, having at AOO happen before you even start casting doesn't affect the spell at all (though of course circumstances where you start casting could provoke an AOO and ruin it).