This actually speaks to the more critical point that inequities in educational opportunities start much earlier than selective-school admissions, or even school entry itself. Attempting to increase equity with quotas alone--whether or not there are subtle discriminatory qualities to the selection process--papers over the true inequities that persist among populations with diverse demographics of many kinds, including both poverty and institutional racism. Access to a selective program at 8th grade will not erase the previous eight or nine years of potentially subpar educational environments both in school and out of it.
That doesn't mean there is never a good reason to look thoughtfully at disproportionality along racial or other lines (e.g., there is a longstanding statistic that students with special needs are significantly more likely to be disciplined, even after controlling for those with behavioral disorders), but solutions should address root causes, instead of artificially changing the outcome markers so policy-makers and institutions can feel better about themselves.
Schools can't change everything about society (although many educators try to help their students on every level, often at great personal cost), but they can choose how they distribute resources and priorities with regard to their own underperforming K-8 schools. Research has consistently found that most parents of students in underperforming schools are just as invested in their children's education as those in more affluent, higher-performing schools, often contributing far more financially, as a percentage of income--but they have fewer resources to work with in time, money and educationally-relevant skills. Improvements there would impact not only the tiny fraction who might move on to selective high schools, but also the other 90+% of students who definitely won't.
