As a rule, “I-statements” are more effective than “You-statements” when it comes to redirecting students. If, for example, you say, “You need to sit down” or “You better sit down,” some students will respond argumentatively—“How do you know what I need to do? Don’t tell me what I need to do.” Other students will be defensive—“I was just sharpening my pencil.” (Never mind that they had moved on to practicing jump shots at the trash can by the time you confronted them.) And then there are those students who will say nothing at all, but instead try to show you (and their classmates!) who’s boss by shuffling or strutting or stomping back to their seats. In any case, it’ll take all the self-restraint you’ve got to avert a drawn-out conversation if not an all-out power struggle.
By contrast, telling students firmly yet calmly, “I need you to return to your seat” carries little if any potential for eliciting discussion, let alone defensiveness or defiance. Instead, students are more likely to accept your request for what it is: an authority figure asking them to do what they themselves know is the right thing to do.
So if you’re looking for cooperation rather than confrontation, you better not say “you better…”