Should I include high school details in Grad School Resume?
I have to disagree slightly with the stark "No" answers.

Only when those details provide evidence of your potential for research.

Some information about your high-school experience may shed light on your research potential.  Certainly you would want to mention winning the Intel Science Talent Search or the International Olympiad in Informatics, or describe the peer-reviewed research papers you published as a high school student.

But your high school grades?  No, leave them off.