Once per turn

I think we have been doing some powers wrong.
Sneak attack says it is usable once per turn. Once per turn powers are usable once on every persons turn.
I think the way we have been playing it is once per round not turn.

once per turn
Some effects can occur only once per turn. If a creature can use an effect (such as a class feature) only once per turn, that effect can be used no more than once during each turn in a round—not only during that creature’s turn.

Once Per Round
Some effects are usable only once per round. For example, if a creature uses an effect (such as a class feature) that is usable only once per turn, it can’t use that effect again until the start of the creature’s next turn.