A problem I see is, that even if there is a problem detected, wether it is detected by some magic sorcery, a "aggression detecting device" or a well trained teacher, it could be quite hard to "get rid" of the problem, at least here in germany where nearly every parent thinks that his child is the best, most beautiful, absolutely stunning child that ever lived, which couldn't do anything wrong in his whole life, so why do you even bother me with this, you dumb, incompetent teacher, and now go on with raising my child. - I guess you know what I mean.
I feel reminded of one particular kid that was in the boyscouts group which I led. It was pretty obvious that he had some issues with aggression, but I had no chance of dismissing him from the journey since his parents already paid for it. Also they were some rich snobs involved in local politics, so you better keep quiet if you want your little scouting thing to keep existing.
However, this kid decided to went on vacation with the scouts. As you might have guessed there are rules, such as "no smoking for children", which should be obvious. Never the less, he smoked. repeatedly, even in presence of the youngest kids we had with us. Taking the cigarets to the leaders tent didn't help, he just took them back as soon as nobody was watching. So I took the cigarets and disposed of them. The next day at the fireplace, said boy had to chop wood. I was working in the firepit as suddenly another one of the leaders shouted at me to duck - which I did, just before the axe that the boy has thrown at me would have hit me in the neck. The wooden shaft still managed to hit my shoulder.
I called the parents, let them pick up the child. A week later I got a letter from the police in which I was accused of stealing the cigarets and the scouts were closed.