SAN FRANCISCO – With a law that spells out the rights of transgender students in grades K to 12 set to take effect in California, school districts are reviewing locker room layouts, scheduling sensitivity training for coaches, assessing who will sleep where during overnight field trips and reconsidering senior portrait dress codes. But administrators, counselors, teachers and school board members also are watching and waiting. The law, the nation’s first requiring public schools to let children use sex-segregated facilities and participate in the gender-specific activities of their choice, could end up suspended within days of its Jan. 1 launch if...