Mayor Michael Bloomberg delivered his final State of the City address yesterday in Brooklyn, touting the across-the-board gains made during his extended tenure in Gracie Mansion.

But one signature Bloomberg initiative, high school choice—designed to offer every child in the city access to every school, no matter where they live—isn’t delivering the “level playing field” the mayor and the Department of Education have long promised.

Instead, more than half of the high-school graduates designated “college-ready” by New York State standards are products of only 20 high schools—less than 5 percent of an expansive, and ever-expanding, universe of more than 550 high schools city wide.

Last fall, the Annenberg Institute documented a strong correlation between where students live and their eventual educational achievement. But if children can go to school anywhere, why aren’t more schools more successful? If half of the city’s college-ready students graduate from a handful of high schools, what does that say about the quality of the hundreds of other high schools that serve New York’s youth?

Readiness the newest metric

All of New York’s high schools are paying increasing attention to the newest education metric, college readiness, which now accounts for 10 percent of a school’s survival-or-bust Progress Grade. But not every school, and not every student, gets an equal shot at readiness.

In New York State, the Regents define “college-ready” as scores of 75 and 80 on Regents English and Math exams. These scores predict basic survival—a C average—in CUNY colleges.

Bloomberg, in his address at the Barclays Center, said one of his accomplishments was that "our college readiness rate has doubled even as our dropout rate has been cut in half."

But according to DOE statistics, only 1 in 5 students in the class of 2011—21 percent of just over 52,000 high-school grads—was considered college-ready.

This lopsided average becomes even more skewed considering the thousands of high-achieving students enrolled in the city’s most competitive, academically rigorous schools: Of New York’ roughly 10,500 college-ready high-school seniors, more than half attended a handful of top-tier public high schools, where grad and college-ready rates routinely top 90 to 95 percent.

That math leaves more than 500 high schools to account for the balance of NYC’s college-ready graduates: That’s very long odds, in a lonely landscape.