Wow! I am absolutely the worst at seeing these kinds of things, even after ya'll eagle eyes see them first and tell us! But this one was so obvious!
I did notice, tho, that Shatner's character wasn't wearing a tie. I am pretty sure that ties and jackets, and dress shirts, were required for male teachers at that time. I'm from the Sourh, and female teachers couldn't wear pants until somewhere around 1970-1972, and they had to be a pantsuit, with the top being longer than fingertip length.
Student girls were the same--no pants until then, and no jeans until 1973, 1974?