Many colleges do take into consideration the high school you go to, because it provides some guidance into how well prepared you may be for college. The high school profile provides valuable information to ad coms. But a ‘competitive’ school is only competitive if the colleges view it that way. I have heard ad coms say, we know an A from high school X really means an A. The implication is that there are schools that are viewed as more rigorous and some that lack rigor. So at a very rigorous/competitive school, the top students may fall beyond the top 10%.