We oftentimes say that we want good teachers and therefore want to hold them accountable for their "performance," while we neglect the student's responsibility in the learning process. A teach with poor discipline is called a bad teacher despite their knowledge and real teaching skills, while students with poor performance blame their teachers, instead of themselves and the behavior of their peers.
Really, a teacher's knowledge is the only thing that really matters in teaching a class and the only thing that can be objectively assessed. Teachers can be taught new teaching techniques, but discipline is an entirely different issue from teaching which should be farmed out to those qualified to discipline. The teacher who is not responsible for the student's grades is free to teach.
Classrooms need cameras in them where others can watch and quickly intervene from outside the classroom. Halls also need cameras for the same reason. By quickly glancing over the monitors, a principal can see the conduct of all and give direction immediately to restore the environment to learning as quickly as possible. Specific students can be watched throughout the day, and weapons or other illegal behavior can be spotted quickly. Messages can be sent to specific speakers to provide minimal disruption of the rest of the school.
Problem students can be easily identified and moved to classes with other problem students, where they are more effectively dealt with. Tests can be more easily and effectively monitored. Discipline can be handled by a more centralized and streamlined authority. Teachers can have a wireless transmitter or other signal that brings attention to the class for swift situational assessment and student discipline.
The evaluation of the teachers can be effectively accomplished with tests and observation of the classroom for professional behavior alone. Movement throughout the school can be managed and controlled by the monitors.