A few days ago we got a form to fill out if we want our daughter to participate in upcoming religious instruction classes. They are generically Christian, on the lines of "learn about the kind of God Christians believe in"; that is, they leave open for the moment whether that god is an ill-defined feeling that everything will turn out alright or the kind that boils you in a lake of molten sulphur for having had impure thoughts.
Anyway, it is interesting to consider the different approaches taken by various countries. Despite being the most religious Western country, the USA are famously officially secular, and so there is no religious instruction in public schools.
In my native Germany, however, there are pretty much official state religions - Lutheranism in the north, Catholicism in the south. Not only does the government collect church taxes from all Lutherans and Catholics, but public schools everywhere except in the state of Berlin offer classes in their locally dominant religion as the default option, with atheists having to actively opt out. At least that is how it was when I grew up, but to the best of my knowledge the only thing that has changed is that some areas have become more open about offering an Islamic option.
Australia, or the Australian Capital Territory at any rate, sits kind of in the middle. As indicated above, there are generically Christian classes on offer in public schools. On the plus side, they appear to be opt-in instead of opt-out and they are run by volunteers, which means that apart from overheads like providing a room etc. no taxpayer money is wasted on sectarian beliefs.
However, this comes with a downside: the classes are run by volunteers. Although I am happy to be corrected I assume that they are unlikely to all have the same standards and pedagogical expertise as trained and certified teachers. Perhaps worse, in contrast to a professional teacher who is paid to do their job, unpaid volunteers are more likely to be motivated entirely by missionary zeal; it is at least conceivable that this self-selection effect will have what I will diplomatically call interesting consequences. And indeed one hears stories...
As should have become obvious, I am in two minds about whether the German professional system or the Australian voluntarist system is better. I am, however, quite positive that of all three I personally would prefer the American one: Just keep religion out of public schools and let the various sects organise religious instruction in their own time.
And what to make of the openly sectarian private schools supported by hundreds of millions of tax dollars is yet another issue.