I went to a state school on the UK, DH went to a private boarding school in Ireland, the DC are now in state-run international schools (ie lessons partly in English) here in Germany. I hate hate hate the German school system, but I suppose in some ways the standards are very 'high', in a very restrictive academic sense.
The state school system is incredibly elitist, with very few comprehensive schools. Everyone else is divided after year 4 (age of 10) into one of three schools - grammar schools, 'Realschulen' and 'Hauptschulen' according to their grades in years 3 and 4. The grammar school is effectively for the children of professionals, the Realschule prepares people for skilled manual work, and the Hauptschule focuses on ensuring people can read and write enough to become labourers or shop assistants. Of course after only 4 years of school the place they end up at is largely reflected by their own parents' level of education.
The school system is largely based on continual tests and assessment rather than actual learning. Grades are everything and kids soon become disillusioned with actually learning content and are simply out to get the best grades - whether they learn anything along the way is irrelevant.
However, DD1 (13) is now in year 8 at a grammar school and I think the actual level of what she is learning is incredible - far more analysis than was expected of us at the same age. She's given a topic - diabetes, Copernicus, Beirut - and expected to produce a fully researched analysis plus competent Powerpoint presentation to the class. I think what she's doing is at a higher level than I had at O-level, perhaps because the school is so academically selective.
The downside is that it's incredibly stressful for the kids, and there's no alternative home schooling (illegal). DD1 has been suffering psychosomatic stomach and headaches, other friends have other stress-based illnesses. The grammar schools have the attitude, 'if you can't deal with it just get out', but obviously the other schools don't prepare kids for university in the same way (and DD1 is pretty academically competent and would get bored elsewhere). So I feel German schools have a very weird, traditional and inappropriate way of defining intelligence and academic success - it's designed to exclude people rather than include them.
The good thing is that the schools only start at 5.6 to 6 years, which gives more time to relax at nursery. In Berlin the last year of nursery before school is now free of charge (sponsored by the state), so everyone can send their child, and get prepared for school. However, very few nurseries teach letters or numbers, so if you don't do that at home your child will be disadvantaged from the start.
And - this is worst of all - the schools start at 7.55 every morning. Surely that's against the Human Rights Convention!