hello, and welcome to the forum.
Yes, at that age your best bet is a private English school.
I have heard great things from Hull School in Zurich.
http://www.hullschool.ch/en/hulls-school/
Their teachers have English teaching qualifications, and go the extra mile to get the kids to pass the exams.
EDIT: i wasn't going to say that the kids wont cut it in the local school, like 22yards did... but i fully agree... sorry