Indeed, and the assertion that 'only poor kids together' will behave even worse certainly needs backing up with data.
It seems obvious to me (since the experiment is repeated over and over within millions of families) that environment plays a major role in behaviour, but tbh I don't see good behaviour rubbing off onto the 'bad' kids in a mixed setting, it's almost always the other way around, or at best, a productive environment is disrupted by a few troublemakers.
So 'good' kids should get an environment free of disruption so they can do what they do. And the 'bad' kids should get an environment much more focused on encouraging good behaviour, so they learn to do the good stuff too. Win-win.
It seems obvious to me (since the experiment is repeated over and over within millions of families) that environment plays a major role in behaviour, but tbh I don't see good behaviour rubbing off onto the 'bad' kids in a mixed setting, it's almost always the other way around, or at best, a productive environment is disrupted by a few troublemakers.
So 'good' kids should get an environment free of disruption so they can do what they do. And the 'bad' kids should get an environment much more focused on encouraging good behaviour, so they learn to do the good stuff too. Win-win.