Tampa, Florida -- Hillsborough County's public schools are under fire for offering some classes and schools where boys and girls are separated by sex.
The ACLU says the programs violate anti-discrimination laws by grouping boys and girls together, then teaching them differently.
They're asking the state and federal governments to investigate whether the district is breaking the law.
10 News went right to Hillsborough Schools spokesman Steve Hegarty for a response.
"These are not new concerns. There's case law and there have been test cases around the country in the past," Hegarty said.
"We were well aware of that when we set these up. So we think we're going to pass muster without a problem."
Hegarty says about one percent of the county's students have a class with just one gender. The programs were set up with help from civil rights experts, and parents always have a choice.
So does teaching boys and girls separately really help them learn? Or does it just reinforce gender stereotypes and actually hurt kids' education?
A breakthrough private school in Ybor City that swears by same-sex classrooms seems to have one reason why they split up the boys and girls.
If you look around Henry Ibanez's history class and you'll see a globe, flags, and plenty of boys.
But you won't see distractions.
"Focus on their academic studies. We have to lay that foundation," explained Lincoln Tamayo, who leads the school where Ibanez teaches.
"When they're coming to us at less than grade level because they have not been held to a high standard, and they're entering their adolescence, we need to develop that focus," Tamayo adds.
Tamayo runs Academy Prep, a life-changing college prep school where underprivileged students go eleven months a year, six days a week, and eleven hours a day.
The middle school is privately funded, but it still has to follow the same Title IX anti-discrimination laws as public schools.
For electives and lunch, girls and boys mix. But when those students are in their core academic classes, they're with only the same sex.
"Almost every single student who graduates from Academy Prep in eighth grade is graduating two to four years greater than grade level in mathematics and reading. And they are succeeding beautifully," Tamayo said.
The American Civil Liberties Union argues splitting boys and girls is based on bad research and discredited studies.
The ACLU outlines its concerns with Hillsborough County's public schools in this formal complaint.
The group says the two sexes don't learn differently, and teaching them as though they are extraordinarily different can get in the way of their development.
At Academy Prep, they're careful to make sure the boys and girls get the same treatment.
"We are holding our girls and our boys to the exact same standards," Tamayo said.
"And if girls get A's and boys get A's. We're not giving the girls perfume bottles and the boys footballs."
Tamayo says he has seen same-sex classes lead to top-flight students for more than a decade at Academy Prep -- with more than 96% of its middle school graduates going on to graduate from high school -- and he's a believer.