Our grade school did not have locker rooms, so we had to wear these lovely things underneath our regular school clothes. The elastic around the legs tended to cut into the flesh of chubby 10-year-olds.
In the mid 70s, I wore pretty much the same thing in 7th and 8th grades. Only mine had shorts on the bottom, no elastic. And it was white, which meant you had to be careful what color underwear you were wearing on gym days, because anything other than white or nude colored underwear would show through and you would get teased to death.
Then, in 9th grade we moved up to the high school, and we just had to wear shorts and a tee shirt.
Then, we moved and I started a new school. Blue and white striped, knit fabric. Sort of a one-piece bathing suit with short sleeves and a blue skirt attached. Just lovely for climbing ropes, as there was nothing on your legs to prevent rope burn. Oh, on rope climbing days, we were allowed to wear sweat pants over the gym suits. Only no one's parents were willing to spend money on something we'd only wear a few times--sweat pants weren't popular, and in addition to the gym suits, we also had to buy school uniforms.
This was the only picture I could find. This one has shorts, mine had a standard bathing suit bottom with a short, solid blue skirt over it, about the same length as these shorts. Seriously, the shorts would have been more modest. http://img2.etsystatic.com/012/0/7882173/il_570xN.434741958_t9du.jpg
We had no locker rooms, so we all changed right in the gym--it was a girl's school, so there were no boys to worry about.
The school basketball team competed in skirts for the first two years I was there. Then they got new uniforms with *gasp*shock*horror* SHORTS. You would have thought the sky was falling. This was in 1976.