It's not about balancing; it's about making use of the untapped resources we have in the less-well-off kids in this country. The greatest factor in educational success is parental involvement. There's no way to change that through policy, no matter what we do. The reason richer schools put up better performance is because the parents there have time to give a damn about their kids' education, investing time and resources into the process. It's not that easy to do this when you have to work two jobs in a row on a given day.
The greatest policy-based factor is consistent time in school. Surveys show that retention is equal across all socioeconomic classes at the end of the year. It's at the beginning of the year, testing over the previous year's material, where the discrepancies arise. That's just because you're rarely going to remember anything you're not interested in if you don't have to think about it for twelve weeks.