What is appropriate though? I considered punishments like lines or detentions worse than CP. Another child (‘A’) might consider CP worse than lines or detention. If I were given lines for a particular offence and a ‘A’ got the slipper, we would both think we’d been treated more harshly than the other. Those punishments might be the most appropriate for each of us (by however you determine appropriateness) but, in that situation, would be almost guaranteed to cause resentment in both of us.
If, however, we both received the same punishment (the slipper), only one of us would think it harsh – the other would consider it being let off lightly. The resentment felt by ‘A’ would be mitigated by the knowledge that he (or she) hadn’t been singled out for harsher treatment.