Do you ever struggle to give a whole-class assessment? Behavior can be an issue. Here's what I do.
Sometimes I have an assessment, say math for example, that I need to give to the whole class but I have to give it step by step, problem by problem, in order to get the best results. Knowing full well that certain kids will answer a problem more quickly than others, I always give the kids a piece of paper to doodle on if they finish a problem early. This little trick saves me every time. Behavior issues are typically a non-issue.
Try it! I bet it will work for you too.
P.S. This also typically prevents them from doodling on their assessment, which honestly, drives me crazy! :)