To date, research hasn’t shown that educational outcomes are necessarily better in single-sex classrooms. A 2005 report commissioned by the U.S. Department of Education identified only 40 methodologically sound studies on single-sex schooling; 35 percent of the outcomes favored single-sex education for concurrent academic accomplishments. The analysis, which preceded the 2006 regulations, didn’t include any public schools in the U.S.

Sax, who disputes the findings in a three-page critique on his association’s website, describes the results as neither exhaustive nor scientifically rigorous. Moreover, assigning boys to an all-male classroom isn’t always sufficient, he says, as teachers need to be taught how to motivate learning. “If the teachers have no training, as a general rule the coed format is preferable,” he says. Sax’s group offers an annual conference and numerous training seminars, and Douglas hopes to train his newly hired teachers through the association before the Dallas school opens.

So can boys and girls be separated without risking harm? Ison-Newsome says that she’s personally struggled with this question, explaining she’s “not a proponent of separate but equal because, as an African-American, I see how that didn’t work.” But she also believes that it’s possible to be “separate and empowered,” saying boys’ and girls’ schools can still compete at debate competitions, among other platforms. Neither should public schools be cookie-cutter in their teaching approach, she says.

Eliot and the ACLU’s Sherwin are not as sanguine. Sherwin says the programs resurrect stereotypes that “really sound like they are coming from the 1950s.” Eliot, for her part, says the scientific proof isn’t there to justify such a divisive educational approach. “It does seem to me that there is a tremendous amount of faddishness in education,” she says. “And this is just the latest fad.”