CP would no longer work, in my opinion – the only schools where there would be a reasonable parental consensus to make CP a norm would be religious-based schools, where most of the children are generally well-behaved and wouldn’t need such measures because their home environment is generally disciplined (and I don’t necessarily mean domestic CP). The kids who always come to mind as “needing a good hiding” would be the ones whose parents already complain about their poor darlings being picked on by teachers and would never sign consent, in addition to which schools would physically be unable to administer CP to a determined well-built child who refused to accept it.