This involves not letting your emotions get the better of you. If you are in a room with 30 screaming seventh-graders and don't yell at them, you're using emotional objectivity. And preventing emotional leakage, where you're mad at one child for what another one did, is also part of it. Finally, recognizing why children are acting the way they are is important.
So, if a first-grader is throwing a tantrum, being objective would involve understanding what the child wants, why they think a tantrum will work to get it, and then acting in an appropriate way to teach the child a better way to get what he or she wants. Yelling, hitting, and duct tape are all examples of inappropriate responses ;)