It's changed over the decades. When I began, most of us new hires were guys in our first semester of college at a time where tuition was affordable with that part time work. Now it's a rarity to find any kid just months out of high school on any of the sorts.I would say the vast majority have a second job even if it is day care or caring for elderly parents.
For awhile, the best path for them to achieve a big bump up in pay was to become PT sup but not all that many want to continue on that path for all that long either.