"Opponents of school choice are running out of excuses as evidence continues to roll in about the positive impact of charter schools," declared the Wall Street Journal last week.

In recent months research has shown that charter schools benefit their own students as well as students in surrounding traditional public schools. Low-income NYC students attending charter schools from kindergarten through 8th grade can nearly close achievement gaps with their peers in the affluent suburbs, 86 percent of the reading gap and 66 percent of the math gap.

Traditional public schools also respond positively to competition from charter schools according to a new Manhattan Institute report. Overall, "for every 1 percent of public school students who leave for a charter, reading proficiency among those who remain increases by about 0.02 standard deviations. Math performance is unaffected. However, the lowest-performing students in a school benefit from charter-school competition in both math and reading," according to the report. "This positive effect, though mild, is encouraging," says study author Marcus Winters. "We can now say with confidence that all New York school children gain from the existence of charters, even those ‘left behind' in traditional public schools."

Nationwide there are more than 1.5 million students attending almost 4,600 charters in 40 states and DC. Charter schools are public schools, abiding by the same admissions and accountability rules as traditional district-run public schools. On average, charters receive about 61 cents for every dollar traditional public schools receive; however, charters don't have the "burden of work rules and other constraints imposed by unions and the bureaucracy."

Such autonomy benefits charter teachers, too, whose satisfaction rates are twice as high as their private counterparts and more than three times as high as their district counterparts. Given the mounting evidence of success, policy makers, including President Obama and Education Secretary Arne Duncan, should work to remove the arbitrary caps and other barriers favored by opponents that prevent the expansion of charter schools.

(This post was co-authored by Evelyn B. Stacey, Education Studies Policy Fellow at the Pacific Research Institute in Sacramento, California.)