By granting a blanket exemption to all girls, no matter how badly behaved or what their individual characteristics are, school ‘A’ clearly doesn’t believe CP is necessary so it’s use on boys is an abuse.
If, as Doctor Dominum has claimed, CP is less likely to be effective on girls and can lead to an increase in misbehavior, the level of misbehavior and the rate of recidivism in school ‘B’ should be higher too. A caning rate of less than twice that in ‘A’ would indicate ‘B’ uses it much more sparingly.