I can see what you guys are saying about bolting/surfacing/panicking, but it's not such a black and white thing. Sometimes a DMT will surface during this skill because their buddy has done something wrong, and maybe they could have grabbed the occy (not the instructor's though - I sometimes assess this with just a snorkel). Either way if they grab the occy or surface, they will be repeating the excercise, and the important thing is they learn from the previous attempt, and are becoming more comfortable and better at solving the problems the equipment exchange can throw up.