The late '60s-early '70s were the transition years here. I went to public high school. Before 1970, it was skirts/dresses only. And no more than 4" above the knee, or you were sent home. (I was threatened several times, but never actually sent home.) In 1970, we could wear pants but not jeans. In 1971, we could wear colored or patterned jeans but not regular BLUE jeans. (I had some favorite red, white & blue striped jeans I'll never forget.) Finally, in 1972, we could wear blue jeans. But we couldn't show our navel. Needless to say, absolutely NO halter tops. Guys pushed the envelope by wearing overalls without shirts under them. (They were sent home, too.) Or sandals with no socks. (Oh my!
)
The next year I went to the state university where pretty much anything was tolerated short of streaking, which was the new "no-no." That was a seasonal thing, though. Nobody really wanted to try it in the ice and snow.