Classroom cameras

In my seven years as a substitute teacher working 140 days per year in grades 6 thru 12 and only high school the past two years, I have seen problem students in every grade level. My anecdotal evidence suggest that less than 3% of students cause in classroom disturbances but those few can disrupt the entire class. I sent letters to three school principal suggesting cameras in the classroom and they all felt it unnecessary. With the onset of computer school a controversy has arisen regarding cameras in the room and some say parents would be upset to see some of the things the teachers are saying that have nothing to do with the subject matter. That may be true but it's my belief that parents would be upset to see how the teacher must spend an inordinate amount of time dealing with one disruptive student. The parents of the other students would demand that the disruptive student be removed so that their children could be in a learning environment but this would interfere with the concept of mainlining students with problems.