There is plenty of evidence that zero tolerance policies do not work and are indeed often counterproductive. I understand they are seductive to some. Many teachers have always thought discipline is a problem. I've taught in a challenging part of the country, including with excluded pupils for several years, and in my experience there has been no change. The loss of experienced teachers however, is a different matter and many younger teachers may now feel unsupported in the workplace if they have behaviour issues. Indeed their management may quite likely lack the experience to deal with such issues competently too. This things do not mean the nature of young people is changing for the worse.