I'm a Swede who's spent many years abroad but am now back in Stockholm. My girlfriend will be moving here next year along with her son, who will by then be 12 years old. She's American by birth but has been living in Europe for a long time. The boy is bilingual in English and German, and in general seems to have a good ear for languages.
Now, the question is what sort of school he should attend. We want him to learn Swedish in school, since he won't be getting much of it at home, and get to know Swedish kids. We're also a bit skeptical about schools that are heavily dominated by expat kids who are likely to leave after a year or two. On the other hand the kid clearly has an international background, he might feel left out if he ends up in a Swedish-only environment, and he will need some support at first before he's up to speed with the language.
I imagine either an international or a normal school could work quite well, largely depending on the actual mix between Swedish kids and expats as well as what the process and available resources would be for him to learn Swedish. On top of that we'd obviously like for it to be a good school in general. We're fairly agnostic when it comes to Swedish curriculum vs some other.
I'd be very interested in your thoughts in general, as well as specific recommendations for schools that might fit the bill. We'll be living on Östermalm initially but would be happy to consider other areas as well.