There is a phenomenon that all public speakers encounter when they are addressing a crowd that if you thought about it very much, it would get to you. It is a phenomenon that any teacher who is trying to impart knowledge to a room full of students will experience as well. And if you think about it very much, it will get to you too. That phenomenon happens when you are talking along and you look out at those blank faces staring up at you and you realize that a few, some or maybe all of those minds behind those faces are paying absolutely no attention to you at all.
Whether or not that drives you crazy depends on whether you consider the act of teaching complete when you speak or when the student grasps and understands what you are saying. Very often when you see a teacher speaking you know that this teacher has absolutely no concern for whether the students are getting it or not. They do not consider it their job to make sure the students understand or interact with the material. They are a delivery vehicle and if they enunciate the lecture successfully, they have successfully "taught".
But just saying words into the air whether or not they are heard or understood really isn't teaching is it? Put it in the context of a chef. If you cook a wonderful meal that is delicious, prepare it with the finest of materials and present it with perfect ambiance, is it still a delightful meal if there is nobody at the table to appreciate it and nobody eats the meal? No, you are only a chef when the patron dines on your food and appreciates every nuance of the flavor and the experience of enjoying what you have done.
That distinction is what drives teachers crazy when they feel students are not listening. To a teacher who has a passion for the real act of teaching, their job is not done until the students grasp the material and interact with it, question it and finally grasp it and make that knowledge their own. A lecture not heard, not understood, not "taught" is not teaching at all, its just talking.
Preparing to become a teacher is about more than just knowing how to design a lesson plan and how to organize a class room and make a bulletin board. Becoming a teacher means you become one of those amazing people who can take students from uninformed to informed and from unenlightened to truly "taught". When it is your calling to become that kind of teacher to just talk at students with no knowledge of whether they know what you are saying at all is absolutely unacceptable.
This means that you will have to change your teaching style. It means that you won't be satisfied with just working through a lecture. In fact, it might spell the end of the lecture as a teaching device for you entirely. To really find out if those kids are listening and interacting with the material, you will have to change your approach to an interactive teaching style. You will have to start talking to students or with students and not AT them. But once you do that, the feed back you will get and the quality of your teaching will improve so dramatically, you will never want to go back.