The advantage of attending high API score scores is having more resources (i.e. the kids are a reflection of their parents who strongly skew to higher incomes) because the parents contribute to them out of pocket, being immersed in a more academically comeptive environment and having teachers able to teach to a higher level because they arent worried about their students not having a safe roof over their heads and full bellies.
There are kids that rise above their surroundings and more limited opportunities and quite frankly I have all the respect in the world for those of them (and you) who can do so. Going to a lower scoring school does not doom you to mediocrity just like going to a high scoring school does not guarantee high acheivement in life. But going to a high scoring scoring school does increase your opportunities to succeed. Why would anyone try to think or argue otherwise?
