Goblinchild I know you are right that a child may argue, lie down, shove, etc but aren't there some children who will refuse at the moment simply because they know they can get away with it?
A request to turn out their pockets or have them turned out by the teacher at the moment is more likely to meet with obstinate refusal because the child knows that, to carry out the threat, the teacher must leave the room to find another teacher (witness/same sex) during which time the object, if there is one, can be removed and either handed to someone else or hidden. If a child knows that the teacher has the power, even if only theoretically, to carry out the threat, there and then, aren't a significant number of children likely to comply?
I know that there are, sadly, a number of children who really won't care and will behave badly anyway but I'm sure that there are a number also who behave badly because they want to "appear" to run with the "bad crowd" but, faced with a bit more authority, would probably buckle at the first hurdle.
In short, I do believe that there are some disruptive children who are such simply because they can be. This new measure, I think, may go some way to "sorting the wheat from the chaff" so to speak and at least cut down the level of disruption. It would also highlight those children who have a real problem with behaviour/anger management etc so that, hopefully, they would get some help?