1. "Native American" is used to refer to, um, uh, Native Americans (the people formerly known as 'Indians'). You can probably just use 'American' or if it's critical that it only include people born in America, try to put it in the middle of the sentence so 'native' doesn't have to be capitalized.
2. from your questionaire: ". . . senior high school students should be able to critically think about social affairs"
i'm pretty sure that in Japan, just as in the US, 'think critically' is a keyword for pushing your views on them by presenting skewed 'facts' and then asking them to 'make up their own mind' on the basis of the one-sided presentation you just gave them
3. your webpage looks really bad w/o japanese font support. see attached screenshot