A teacher is a gatekeeper, someone who presents a subject in its most interesting form so that individual students engage with it, understand it, and contribute to it.
In this, a teacher's main tools include recognising where each individual student's attention is, engaging it and directing it repeatedly onto the most interesting and key simplicities of a subject until a connection between the individual student and the subject has been established, and then constructing a bridge deeper and deeper into the subject's heart so that the student comes to know the material rather than simply 'know about' it.
This bridge to knowledge is made by making sure that the subject is as interesting as possible, by clearing misunderstandings out of the way, and by moving forward at the most optimum pace.
To put it another way, knowledge to a child is an unexplored kingdom with an empty throne. Wisdom is the map.
Choosing the right syllabus, selecting the best text books, devising the most engaging schemes of work, providing the necessary amount of reality in lessons, and attracting attention through carefully planned and run lessons are part of what a teacher must do to get the product of a more knowledgeable student and a wiser student.
There is no such thing as a difficult student; there is only a failure to recognise where a student's attention is, followed by a missed attempt to redirect it and a lack of success in removing obstacles in the way of that particular student.
Students who are trying to engage with subjects but failing can and should first be addressed in lesson as this is the primary action of a teacher -to connect the student with the subject. Only when this becomes too difficult within the confines of a class-based lesson should specialised additional resources need to be involved, and then only until individual barriers have been addressed sufficiently for a student to return to class.
A student whose attention is recognisably not anywhere near the subject -as indicated by disruptive behaviour- needs to be addressed both inside and outside a lesson environment through reason and ethics to recover that attention and restore it to the field of learning. Then particular barriers can be dealt with.
The whole structure should be there to connect students to subjects and bring about a state of affairs in which individual students are in tremendous affinity with a range of subjects.
That is education.