According to the U.S. Department of Education's blog, Homeroom, on May 13, 2016, "the U.S. Departments of Education and Justice released joint guidance to schools explaining how federal law prohibiting sex discrimination affects schools’ obligations toward transgender students." The Department of Education "also released a compilation of examples of ways that schools across the country are already successfully supporting transgender students."
The guidance letter "identifies the key requirements that schools need to keep in mind to comply with Title IX and other federal laws." A condition of receiving Federal funds is that schools comply with the requirements of Title IX.
Both documents are available from the Homeroom blog.