Anyone hearing the ACLU’s position on single-sex education would think something troubling is afoot in almost every town in America. The ACLU claims that single-sex education is an unlawful form of discrimination and that its supposed benefits are based on pseudoscience.

In a supposed conspiracy to oppress children, the Catholic Church operates hundreds of single-sex schools across America. A handful of states have opened boys’ and girls’ schools themselves. The ACLU’s lawyers allege that this practice amounts to gender apartheid, a misogynist attempt to hold women back.

Yet children, regardless of sex, would better succeed academically and socially if they were free of the distractions and challenges of chaotic urban schools. The Catholic schools, public charters and public district schools that offer single-sex education offer an alternative to the status quo.

Luckily for Maryland, Sen. Barbara Mikulski, herself a product of a Catholic all-girls school, is a warrior for common sense on this issue and wants to give states the right to educate their children effectively, including the Old Line State. Annapolis should seize on Ms. Mikulski’s leadership and encourage failing schools to try single-sex education. Research, no matter what the ACLU says, suggests that it helps both boys and girls achieve academic excellence.

In 2001, Ms. Mikulski joined with three other female U.S. Senators — Democrat Hillary Clinton and Republicans Susan Collins and Kay Bailey Hutchison — to amend the No Child Left Behind Act to allow states to operate single-sex schools.

Maine, Alabama, South Carolina, Texas and other states took the opportunity to try the school model, and it worked. Today, more than 500 public schools offer single-sex classrooms or schools.

A 2008 report by the U.S. Department of Education found that teachers and principals believed single-sex classrooms facilitated learning by decreasing distractions and improving classroom dynamics and student achievement. A 2009 UCLA study found that all-girls’ schools graduates were more confident and outperformed their co-ed educated female peers in math and public speaking.

Opponents like the ACLU cite other studies that find small or no difference in achievement for girls. What these opponents rarely admit is that almost every study of single-sex education finds that boys placed in single-sex schools outperform their male peers.

The real school crisis in Maryland is a crisis among boys. Boys are 50 percent more likely to drop out of high school than girls across all racial groups. In Baltimore City, boys consistently lag behind girls in both math and reading from 3rd to 8th grades on the Maryland State Assessment. By 8th grade, girls in Baltimore outscore their male counterparts in English by 12 points (65 percent to 53 percent) and by 5 points in math (60 percent to 55 percent).

The debate over dueling studies ignores something even more fundamental: parental choice. Early 20th century education reformer John Dewey observed, “What the best and wisest parent wants for his child, that must we want for all the children of the community. Anything less is unlovely, and left unchecked, destroys our democracy.”

The parents of students in Maryland’s failing schools deserve that choice, made consciously and freely, to educate their children in the environment that best fits their children’s own needs. The ACLU’s lawsuits to shut down single-sex education should not scare Marylanders but bolster their commitment to expand opportunities for all of the state’s children.

Annapolis would be wise to give the children of Maryland the same opportunities that formed Barbara Mikulski and made her a passionate supporter of single-sex schools. It’s about fairness and opportunity: let the parents decide, not the ACLU.

Christopher B. Summers is president of the Maryland Public Policy Institute, a nonpartisan public policy research and education organization that focuses on state policy issues. His email is csummers@mdpolicy.org.