In an elementary school is it okay to (read details)?

Now, I heard that in elementary schools, they feel your spine. This is around 5th grade. This time the school nurse does it. This time the girls had to take off: Shirt, undershirt, and (if she has one) bra. They do this during phys ed. I think. The nurse feels her spine for something, like bone mis growth. Do they check their parents for this? Is it illegal if not checked okay with parents? Why can't the personal doctor do this? Is this true? Please answer accurately! :D