The use of schools to solve other social problems that arise when children cannot easily or comfortably be supervised by their parents, causes many more problems in the schools themselves. The need to fill a complete timetable, and to follow to some degree the model of the public boarding schools, coupled, naturally enough, with the desire of government to control growing minds, led fairly quickly to the creation of subjects which should not be taught in schools at all. If they were removed from the timetable, the school day would be much more reasonable, could address its real aims more clearly, and some activities which children learn to hate could be understood as fun.
Much of what schools do is unnecessary. Many subjects should not be taught, some because they are simply a waste of time, like religion, ethics, ciudadanía and the other ways of telling people how they should behave according to some fashion or other, and some because they are far better provided in another way. Churches are always willing to instruct the young in their beliefs and codes, and sport and the plastic arts are far more enjoyable if done freely at a municipal or private facility rather than under the full disciplinary structure of a school as they now are. Within useful subjects, a great deal of time is wasted with unnecessary material and in attempting to measure knowledge, rather than provide it and teach how to use it. And of course, the biggest problem of all is that many of the people who are forced to be there are not in fact going to benefit from it, but their presence will prevent others from benefiting.
There is no reason for schools to teach religion, unless that is one of the specific purposes of the school. Otherwise, it is a waste of time. Parents who want their children instructed in their own faith, or in some other, will find plenty of people willing and able to do it for them, freeing children two or three hours a week.
I am not, of course, suggesting that children should not study their parents' religion, or that they should not do sport or learn art. The point is that schools are a bad place to do it.