https://www2.ed.gov/about/offices/list/ocr/t9-guidelines-ss.html
Guidelines regarding Single Sex Classes and Schools
https://www.ed.gov/news/press-releases/education-department-clarifies-requirements-offering-single-sex-classes
Education Department Clarifies Requirements for Offering Single-Sex Classes
To offer single-sex classes or extracurricular activities, schools must:
Identify an important objective that they seek to achieve by offering a single-sex class (such as improving academic achievement);
Demonstrate that the single-sex nature of the class is substantially related to achieving that objective;
Ensure that enrollment in the single-sex class is completely voluntary (through an opt-in, rather than an opt-out, process);
Offer a substantially equal coed class in the same subject;
Offer single-sex classes evenhandedly to male and female students;
Conduct periodic evaluations at least every two years to ensure that the classes continue to comply with Title IX;
Avoid relying on gender stereotypes;
Provide equitable access to single-sex classes to students with disabilities and English language learners and,
Avoid discriminating against faculty members based on gender when assigning educators to single-sex classrooms.