Hanushek researched educational systems that do and don’t track and found that eight out of the nine countries in his study that track students before age 16 see that the difference between highest and lowest test scores is significantly larger than the range in countries that don’t track. (He did not examine the U.S. because it doesn't have a nationwide policy and tracking is most common in high school.)

The 1980s and 1990s saw an influx of research in the U.S. suggesting that while students in upper-level, college-focused classes may be served well by the separation, the students in lower-level classes were suffering disproportionately. Not only did they start behind, but the difference in instruction also gave them little opportunity to catch up.

The No Child Left Behind Act of 2001 required schools to focus on struggling students and raise proficiency by focusing on test scores, which prompted many schools to separate out children who were behind so they could provide targeted instruction. This led to an increase in de facto tracking in younger grades, Theokas said.

It’s a fact of urban life that parents with means will go to great lengths to get their children into the best possible programs, says Joyce Szuflita, a consultant for New York City parents trying to navigate the educational system. New York practices an extreme form of tracking, with students able to test into special “gifted and talented” schools when they're as young as 4.

Not all the parents who hire Szuflita as a consultant want their child in a special school. But generally speaking, Szuflita says, “all parents think their kids are brilliant.”

The U.S. federal government’s push to turn the tide of classroom inequality has intensified in recent years. Over the last three years, the Department of Education’s Office for Civil Rights has resolved cases in 16 districts, all of which are racially diverse and serve student populations ranging from 7,000 to more than 60,000. The civil rights office currently has 40 similar cases under investigation, according to a spokesman.

In those districts, the agency has identified unequal racial representation in gifted and talented programs, advanced placement courses, or other upper-level classes. Such probes typically result in agreements that give the districts a few months to review the policies and practices in schools and identify inequality in upper-level courses and, subsequently, less than a year to come up with a plan to rectify the shortcomings. The federal department must approve the process, as well as the measures the school plans to take.

Theokas says that this individualized process makes sense, as opposed to prescribing the same fixes across the board. “Understanding the problem is the right first step,” Theokas said. “I think that they [the Department of Education] have a bully pulpit, and that they should use it to highlight the … opportunity gap problem.”