That was in 5th grade in my school. An Italian girl named Kathy cast some shadows at high noon, and, of course, we all noticed. And yes, we all stared. I know she was self-conscious about it, because she always seemed to have her arms crossed against her chest.
I was in Catholic School,in the 60’s, in 5th grade, when the girls started changing in shape. There was a well believed rumor, that a girl could get pregnant, from sitting next to a boy, on the school bus ;)