How can I motivate my 2nd graders to stop wasting my time and theirs?

Start rewarding the kids that don't waste time and make a big production out of it. "Look cl, Sally is doing exactly what I asked her to do. Good job Sally. Here is a coupon for free ice cream at lunch" or "Here is a new sparkly pencil" or "How would you like to be the leader today?" or "Sally, pick a friend that is also doing what I asked and you guys can have 15 minutes to play a game." Soon, all the kids will want to be praised. Once they all follow directions, wean them off of rewards and make the behavior intrinsic. Hope this helps...