When I step into a room full of elementary students, or, for that matter, middle school or high school students, I figure on a few things. First, I figure there is bound to be a student who is going to be a smart ass. Second, there is bound to be one who is ultra-helpful. Third, there tends to be, in any group, that one who gets their feelings hurt very easily. Over the past few years, I have figured out how to adjust to these student types (I have not done any kind of scientific research on this, and I in no way endorse the following as the appropriate way to handle students)
For the smart ass. I tend to be fairly quick-witted (especially when compared with grade school kids) and that helps. I often will take the initiative when I find a smart ass. Once one is identified, I await their attempt to gain control of a situation. I am prepared with a quick remark or retort that often puts them in their place without damaging their feelings or their status. In fact, it often makes me a semi-celebrity with the kids. It also helps that I don't take things personally. I figure if I am willing to give kids a bad time, I should expect the same in return. That does not stop me from expecting respect from them. You can tease someone and still show them respect.
The ultra-helpful child often tends to be right there in the middle of everything you are trying to do. They will offer suggestions concerning how their teacher does it. Often the child will offer their services to do ANYTHING at all. No matter how much you want to tell the child to "get the heck outta here!" The best way to combat (Sometimes it feels like a fight) the ultra-helpful child is to give them a job. It makes them happy, gets them out of your hair, and sometimes ACTUALLY helps you! Often it is as easy as asking if everything has been picked up off the floor or even asking if they can hand out some papers.
The final student type, for today, is the child that cries. I sometimes get them. Most children are apt for it, but the best way I have found to prevent it is to announce early on in the day that I don't like kids and I don't consider my work done unless I have made one child cry today. Usually, the kids ask, "Why'd you became a teacher, then!?" I counter that I like to torture children and make them cry. It is at that moment that all children are hardened against any possible occurrence of crying. Of course, they know that I like kids, because they often tell me so. It doesn't matter how many times I deny it, they kids seem to know I DO like kids. They take it as a challenge to be tough. It's a game.
By the end of the day all is well. The kids go home thinking Mr. H is just a cool substitute, but we all know I have just survived another day!