New York City's public school test scores have seen a vast improvement, lauded by Mayor de Blasio and other officials, but the Wall Street Journal points out that the "dirty little secret" in the academic progress is charter schools.

Mayor de Blasio, of course, is a foe of charter schools, as is Democratic presidential nominee Hillary Clinton (who was for charter schools before she changed her mind and garnered a coveted endorsement from the ardently anti-charter 1.6 million-member American Federation of Teachers).

The Wall Street Journal notes:

According to new state testing data, citywide student proficiency increased this year on average by 7.6 percentage points in English and 1.2 percentage points in math to 38% and 36.4%, respectively. Some have attributed the city’s gains, which mirror those statewide, to shorter and easier tests.

Yet strikingly, proficiency at charter schools this year jumped 13.7 percentage points in English and 4.5 percentage points in math to 43% and 47%, respectively. In other words, charter students have improved by two to four times as much as the citywide average.

A recent analysis by Families for Excellent Schools found that New York City charters, whose student populations are more than 90% black and Hispanic, raised their local community school district proficiency rates by 13%. More than 70% of charters outperformed local district schools in math and English. Black and Hispanic students who attended charters scored 73% higher than their counterparts at district-run schools.

Nearly 40% of the top 50 scoring schools in New York City this year were charters compared with 12% in 2013, the year Mr. De Blasio won election. The reason: Student progress at charters has exceeded even high-performing traditional schools. For instance, 82% of students at Eva Moskowitz’s Success Academy passed this year’s reading tests, up from 68% a year ago. Success Academy ranked in the top 0.3% of all schools statewide in math and top 1.5% in English.

American schools are in abysmal shape and the charter school movement seems to offer hope and a way for kids, especially low-income kids whose parents can't afford private schools, to get a good education. And yet De Blasio has done everything in his power to make life difficult for charter schools and Hillary Clinton, if she reaches the White House, is unlikely to lend moral support to this promising movement.

Currying favor with the powerful teachers' union matters more to progressive politicians than educating children.