I disagree. Maybe they aren't going to have a deep discussion about Das Kapital or something, but there are a lot of philosophical principles that can be taught in pretty simple terms. I wish philosophy was required in high schools and colleges here in the US. I think there are very few other subjects that can get provoke as much discussion and thought. The huge caveat here, however, is that to teach good philosophy requires a good (well read, especially) instructor, which, I'm afraid, is probably not available in many high schools.