I can't imagine students walking into class in a pair of striped flanellettes, although less and less surprises me these days.
I think what is being referred to as "pajama fashion" are lightweight, (often plaid) flannel or soft cotton draw string, elastic waist pants. Unlike sweat pants, they have no elastic at he cuff and are cut loose in the legs. I know college kids that wear them to classes with regular t-shirts. Big deal: at least they aren't showing the cracks of their a$$es! Geeesh..I remember the late 60's early 70's: We had to organize an entire school movement to be able to wear JEANS in the winter months. We were told if we wore blue jeans to school we would be suspended. So we organized the entire student body to wear jeans on a certain day: it worked. Who cares...as long as the clothing is decent and doesn't pose any safety hazards---