Hi,
I actually asked an admissions person about this during an interview. I am not sure if this is the case at all schools, but from what he was saying, it probably seems to be the case. For the most part, you should refrain from placing down highschool related activities. You only have so much slots for that kind of stuff on the AMCAS for college ECs and others. The guy I spoke to said that unless you did something outstanding during highchool, it is best not to put it down. I do recommend you know what you did during highschool. One interviewer I had asked me ALOT of questions about highschool. He asked me my SAT scores, what I was involved with (that was hard to remember), class rank, exps there. So I would recommend you at least know what you did. This is just from what I was told and it does make sense, Adcoms are more interested what you did during your college years. This is just my exp and I could be wrong. Either way, good-luck!
David