As rewarding as it truly is, it can be frustrating to spend long periods of time with any number of kids. Teachers and parents need a toolbox full of skills to help them stay calm and reasonable during long days-- and those sudden moments that spring up during a day.
One of the easiest things to do is just take a deep breath and count to ten slowly. While you're counting, try to look at things through the other person's eyes. Both sides (almost) always feel justified in their choices of behavior. If you're calm, it's easier to find a positive solution everyone can live with. Feel yourself relaxing when you count. If you need to, imagine someplace nice and soothing. Once you have your resources gathered, you can check your own perceptions: does the situation really warrant what you're feeling? Are you assuming something, imagining the worst, misinterpreting? Look at the situation, and the person on the other side. Remember, if you're calm, and talking in reasonable, gentle tones, the other person will calm down too. And that means you have a better chance of a constructive solution.