Tries to be clean, ends up wanting to get filthy with his crush. many such cases. GLAD!
Its (was?) very common for students to use classrooms for changing, so she wouldn't have thought much about it. That would be where her bag/cubby would be.
This is much more common in lower grades (i.e. not highschool), and in schools that used to be single sex and are now coed.
They aren't 'in the game' anymore but I had friend who did JET and said in the older/rural schools its more common as it saves time vs herding everyone to the locker rooms - provided those exist. Sometimes the rural/older schools don't have locker rooms, or it might be a single-sex school and only have one so they have to coordinate. Its also more common for elementary/middle school, highschool they'll usually have them use the locker rooms for PE but again that's provided they exist.