Want a guaranteed spot in Washington, D.C.'s best public elementary school? All it takes is $875,000.

With 91 percent of its students proficient or better in reading, Janney Elementary School is the best elementary school in Washington. But the school is located in Washington's Tenleytown neighborhood, where the homes are among the most expensive in the city. The median price for a three-bedroom home within the school district's boundaries is $875,000, well above what a low-income family can afford. Only eight other public schools in Washington are located in districts with more expensive housing.

This exemplifies what has long been true about the old-school model of traditional public schools: The upper-class can afford private school tuition and the middle-class can afford to live in neighborhoods with quality public schools. Low-income families, meanwhile, get trapped in failing schools. That's why school choice is so important — it gives students in low-income families a chance to escape failing schools and get a high-quality education tailored to their needs.

While school choice advocates hope to give low-income students more options, defenders of the status quo are fighting for a system in which only wealthy families can attend the best schools.

The chart below shows the relationship between a Washington elementary school's test scores and the median sale price of a three-bedroom home in the school's boundaries.

The chart was put together by Ginger Moored and posted on the blog District, Measured.

Fortunately, Washington has a couple of school choice programs that help families escape the expensive-homes-for-quality-schools connection. "Around 44 percent of the District's public school students attend a public charter school," Moored writes. "Students earn the right to attend a charter school through a lottery; where they live is not a factor."

The D.C. Opportunity Scholarship Program funds tuition and fees for low-income students to attend private schools.

Moored also mentions that some low-income families can rent homes or apartments in the areas with better-performing schools, rather than buying a three bedroom home, as the chart displays.