Jeans definitely would not have cut it back then.
Back when we were growing up, many schools had strict dress codes. There were plenty of rules of dress that you just simply could not break, no matter the weather. Other standards were not rules exactly, but we tried to follow them none the less. Clothes or hair out of place could have gotten you sent home back then and we didn’t borrow trouble.
If girls wore pants, they were slacks or pedal pushers, not jeans. In winter some girls or young ladies were permitted to wear pants under their skirts for warmth. Shorts were often not allowed for girls.
We wore collared shirts or sweaters and few people came to school or work in a t-shirt.
Limited make-up and nail polish was permitted, if any at all.
Young men wore slacks for the most part, not jeans, unless you grew up in a farming area. In that case sometimes the rule was relaxed.
Everything had to be ironed and you didn’t show up with unkempt clothes.
We wore Bass saddle shoes, Buster Browns, or penny loafers for the most part.