And who were the teachers? Did it cost money, how much? How long ago? I guess the students were motivated and disciplined? Who were the other students? Natives, you mean swedes?
The teachers was often Japanese teachers. Usually they did teaching locally (in Sweden) or had other jobs, but most of them with a teaching license (in Japan). My Mother also did teaching there for a short time, and told me that the salary was very very low (like 300$ or something, per month) and people mostly did it for passion or part of the community thing.
I did a quick googling and right now the price seems 100$ for entering the school, and around 850$ per year. Not sure about the teachers salary now or what back then.
Other students were either: Half-Swedish/Japanese, settled in Sweden. Immigrants with both parent Japanese, settled in Sweden. Expats kids (usually in Sweden for a short time, 1-2 years, for work) both parent Japanese. The former two spoke both language, the latter only spoke Japanese.