Actually we do have legal separation of church and state. But what we don't have a lot of, is religious fundamentalists or the obsession about the constitution that some Americans have. One seldom hears the dutch phrase for 'unconstitutional' for instance.
Well, that latter is because
the Dutch constitution is not "the supreme Law of the Land" as it is in the US. Article 120 of the (current) Dutch constitution reads:
The constitutionality of Acts of Parliament and treaties shall not be reviewed by the courts.
The idea behind this was that the framers of the constitution couldn't anticipate developments in human society, and therefore a potentially outdated constitution should not be allowed to trump an Act of Parliament, thereby sidestepping the whole "Settled Law or Living Document?" question which plays such a prominent part in the US.
There are three categories of schools in the Netherlands: public, private (
very rare) and religious. The latter are nominally private, but they receive government funding as a result of the
Schoolkwestie (school question) back in the late 19th century, in which working class (hardline) Calvinists demanded the state provide them with the means to educate their children in the environment they wanted. It's a long story.
Ultimately, what it boils down to in the Dutch system is that, to complete your secondary education, you need to take a central written exam, the curriculum for which is set by the state. Aside from that, individual schools have a fair amount of autonomy in what they teach and how they teach it, as long as they prepare their students for that final exam. Here's the kicker:
the state biology curriculum makes no mention of evolution. Most schools teach it anyway, but technically, no school is legally obliged to. This is because there's a sufficiently vocal core of hardline Calvinists that lobbied hard to keep evolution off the curriculum.
However, that's also why ID will never get off the ground in the Netherlands; the hardline Calvinists, and any other religious extremists, don't need the fig leaf of ID, since they can already teach Creationism outright and ignore evolution altogether. (Mind you, there's not many schools which do that. Back when I was still living in the Netherlands, I would often take the train between The Hague and Utrecht and be bemused by the presence of bunches of obviously Calvinist teenage girls. It took me a while to figure out that they had to travel halfway across the province to go to school.) Of course, in return for being left alone, they have to leave others alone as well. If the minister of education starts getting too earnest about putting ID on the curriculum, you can bet someone's going to say "sure; you won't mind us making the teaching of evolution mandatory as well then, will you?"
Oh, yeah, I'm Dutch by the way. I just live in the US.