I can see both sides. I think it really should be the parent’s decision as to whether their child is capable to ride to school. After all, they are likely to have much more experience in assessing their own child’s ability. It requires a degree of common sense. However, common sense seems to be lacking from lots of parents these days. Schools know this and are just trying to cover their own backs. It does seem a bit silly to introduce such a rule though when there is no immediate facility to pass such a test. It’s like the government suddenly shutting down a driving test centre! From a practical perspective it isn't possible to run the tests all the time, however it isn't fair (or very pro-cycling) to deny this facility quickly either when such regulation is in place! This brings us back to good old-fashioned parental responsibility!
Despite all the training, bicycles are not really dangerous in comparison to most vehicles on the road. As I understand it, the cycling proficiency test is designed to help children cope with vehicle hazards. When it really takes a car/bus/lorry to seriously injure a child then why penalise them?