Charter schools have been roundly criticized as unnecessary, inadequate and harmful to traditional public schools. They’ve been feared as a potential back door to racial segregation.

But a new study by the Center for Research on Education Outcomes (CREDO) at Stanford University found that not only are charter schools making slow but steady progress across the board, they are of particular benefit to low-income, disadvantaged and special-education students.

Indeed, more than half of charter school students live in poverty, and the numbers are growing. That is a higher proportion than in the country in general.

Some educators suggest that this measured academic progress is a disappointment and that charter schools are not delivering what they promised. But according to this wide-ranging study from a highly respected institution, charter students are surpassing those in traditional public schools in reading gains and keeping pace in math gains.

In 2009, charter school students were the equivalent of seven days behind traditional school students in learning English. The new study shows that charter students are now eight days ahead of traditional school students in learning English.

The study looked at charter schools in 25 states, New York City and the District of Columbia. South Carolina is not included, unfortunately. It would be interesting to factor in success stories like the Charleston Charter School for Math and Science.

CREDO’s results show that more than 6,000 charter schools were serving about 2.3 million students in the 2012-2013 school year. This represents an 80 percent increase in the number of students enrolled since 2009,

One reason for the charter schools’ improvement is that some low-performing schools were closed — about 8 percent of the total. Also higher performing charter schools are being added.

This could be an indication that districts are getting better at discerning quality before a school opens. Another way to further improve charter school performance would be to weed out schools that aren’t performing. But that tactic would need to be used with extreme caution, particularly in districts that have proven hostile to charter schools.

It’s satisfying that charter schools are progressing and that vulnerable students are benefitting in particular.

It’s satisfying that some educators are learning, albeit slowly and reluctantly, that charter schools can play a positive role.

But even where educators are loath to concede their value, charter schools give parents and students choices that they never had before the charter school movement.