Ah, now I see what this is all about: protecting the teachers' union.
That and, as someone pointed out by citing a sentence or two from the ruling about 320 posts ago, about monopolizing the values indoctrination of the students -- brainwashing them for purposes of the Hive Mind.
The next step would be to penalize parents for teaching, or attempting to teach, moral values at variance with those laid down by their children's liberal brainwashers.