Earlier quoted context omitted.
It's pretty simple. A lot of kids don't have an opportunity to put in the time and effort. Some of them still do well despite this, and that shows they have great potential if given the opportunity. Taking life challenges and starting points into account is more of a meritocracy, because you are accounting for the difficulty they had to get to where they are. For example, say you have two kids with the same high SAT…
There's always a lot of weird circumlocutions around "merit" and "opportunity." In NYC, the poverty rate is higher among Asians than among African Americans or Latinos. In what way do the latter groups have "less opportunity"? Is it simply that Asian kids only succeed because they cheat by studying more?
Also with regard to how other groups might have less opportunity, it could be a result of harsher institutional racism towards one group of minorities versus another even given the same socioeconomic circumstances.