Consider a not-so-uncommon scenario from a traditional American school setting.
It is the last hour of the day, and every student in the school has a study hall period. You, the teacher, are supposed to ensure that your students are completing homework, studying, working on projects, or at the very least reading. One young man in the class has picked up a classroom laptop and says he is working on a project for science. You suspect otherwise. This boy is reknowned in the teacher's lounge: he hates school, doesn't do well in any subject, disrupts classes, sasses at teachers, and is probably going to drop out in the next year or so. You're quite sure if you wandered by and took a look at his laptop, you'd find he's playing solitaire -- or something else less tame and intellectually taxing. But he's sitting quietly with his laptop in the back of the classroom, and the room is calm.
What do you do? Well, what you choose to do depends on your goals as a teacher.
If your goal is to have an easy life, to get through your day with as little trouble as possible, you will ignore the boy as long as he is not disrupting anything. If he doesn't get his homework done, he'll bear the consequences of that himself.
If your goal is to be loved by your students, you may join him in his game. Actually, you probably never require your class to study at all anyway. You probably let all your students talk and play games during their study hall time (which is unfortunate for the students who really need that quiet time to get their work done).
If your goal is to maintain control and be obeyed, you will most definitely go check out that boy's computer screen and tell him to get to work. You will hover around him off and on for the rest of the period, initiating a game between the two of you where he tries to find a way to do what he wants to do without you noticing and you try to catch him in the act -- all of which amuses the other students tremendously and distracts them from their studies (more "disobedience" and "disrespect" to deal with). [Confession: this was me twenty years ago. My greatest fear was losing the respect and control of my students. I still have nightmares of teaching a class where nobody is listening to me . . . ]
If your goal is to make a difference in your student's life, you may sit by the boy and engage him in gentle, loving conversation: what homework does he have? Why not do that? Why do you dislike science so much? What do you want to do with your future? What do you like and do well? What are things like at home? You may eventually get him to get out his science book and get started on his assignment, talking him through it to help him, because school is a challenge for him. You may commit yourself to do this for the boy everyday, because you want so much for him to succeed in school. Meanwhile, the other 29 kids in your study hall will be doing who-knows-what while you focus one-on-one with this young man . . . and the next year, when he doesn't have someone spoon-feeding him, your project child will end up dropping out anyway.
Teachers are given an almost impossible task -- take these 25 kids (over a hundred in the upper grades) with a wide range of abilities, learning styles, backgrounds, experiences, degrees of parental support, and interest in your subject area . . . and ensure at the end of the year that they ALL have mastered the material expected to be mastered at that grade level. And at the same time, build their characters and self-esteem. And make sure they love learning. And do it all without the appropriate resources necessary to succeed at that task.
It's no wonder there are so few excellent teachers in our schools.