rowan wrote an answer about Black Diamond Lost Arrow Pitons - DO NOT USE on February 15, 2012
i would trust a sling around a sizeable branch over a piton hammered into wood. if you're just teaching them correct technique for placing pitons, fine. but i wouldn't climb on it. creative problem solving is an important skill to a climber. maybe the best thing would be the toss the rope over the that first branch, adding a sling as the climber progresses. this brings back thoughts of a favorite climb at City of Rocks, Columbian Crack. its a classic hand crack that starts with what seems like an unprotectable chimney behind a boulder, solution: toss the rope over the boulder climbing 15ft to the first protection on TR.