I cannot speak for German, but all four of our children went, cold turkey, to French-speaking elementary schools in various countries. For the first year they spoke not a word of French. Beginning almost the first day of the second year they were more or less fluent.
One, today, is married to a French husband and has two very young bilingual children, in San Francisco. Another has two school-age children in the Lycée Français de San Francisco. A third has a child in the French Nursery School in London, and plans to move to Montreux (where, when I spoke to the school and mentioned the child was a Swiss citizen I was told "never mind that, we have children (many of them) from all countries"). The third, who has the best of all the four in terms of accent and mastery of literary French lives in Oxford and will send her sons to Eton.
When two of our children were at the Ecole Internationale de Genève, Section Française, they took classes in German but were told, in effect, not to worry their pretty little heads about the language, the more so since they spoke English. (They got As or A*s in German GCSE in the UK, but that's not worth much.) That's more or less the story in this article: http://uniset.ca/naty/hebdo_allemand.htm More's the pity: those who learn multiple Swiss languages can aim for senior civil service jobs or politics. (My grandfather told jokes in all three, on stage, in Vaudeville. My uncle spoke Romansch too. But he was Executive Head of Room Service at the Plaza Hotel, New York.)
Hello. I made the decision to send my eldest (still teeny) to ICS this year because we speak absolutely no German and are not sure where we will be in three years time. We absolutely love the school, the teaching, and the opportunities it offers and she is incredibly happy there. I didn't worry so much about her progress in a local school – but I was very concerned about mine! I didn't feel I would be able to help with homework, communicate effectively with teachers or have kids over for play dates and be able to talk to them properly. So there is potential to send your children to the local school and not integrate too! (I am waiting for the groans). Right now, she has friends from all over the world, and I feel she is so lucky to experience so many cultures at such a young age. As I learn the language better, I would consider sending her to a local school – mostly because I hate seeing her in playgrounds attempting to make friends with no joy. However, Swiss German is already creeping into her every day language from the school lessons and our day to day lives, which is lovely to see.
People so far has really given a good suggestions on the international schools. I am residing in Zurich from past 2 yrs and my daughter goes to ISZN school located in Wallisellen. It's a good international school. My daughter is happy studying here.
As you are happy with your decision I am not sure if you still look at this chat. I hope you do. We are moving to Switzerland soon and have a hard time to decide between ICS (Zumikon) and ISZL (Zug/Hünenberg). Should we go for the big school with the choice of AP / IB in Zug or the smaller school that feels more sheltered in Zumikon. We have kids in primary and highschool. ISZL could offer more choices in the curriculum but in a big school there is usually more pressure. On the other hand ISZL is in a rather quiet area on the country side and ics is very close to Zurich and there are unfortunately to much party opportunities around and kids move very independently through the city. My question is, in which of these two schools they will develop academically better, they will feel comfortable, welcome and find all the support they need for great academic success. I have to say that they are good and very motivated students and I don't want to risk anything that could put them away from the path.
Is it possible you typed it the wrong way around? ICS in Zumikon is a big school.
It is likely the area you choose to live in will also have a big impact - those two schools are quite far apart.
When I was looking at international schools, I personally found it illuminating to ask each of the schools precisely how many children were already enrolled in the relevant grade. At one of the schools I contacted, whose website made it look much like the others, it turned out there were only a handful of children in grades 6-9 combined.