edit: The data justify this hypothesis. School enrollment in July skyrocketed from 10% in 1984 to 42% in 2016, and enrollment in advanced coursework has a similar curve to it.

Anecdote time: I grew up in an area with a good mix of blue collar and white collar families. Reunion season is coming up so I reconnected with some old friends. There's actually strong INVERSE correlation between "had a typical summer job" and "success in the marketplace". Most of the doctors/lawyers/engineers/software people didn't work typical teenager summer jobs and are now doing very well, both financially and in life (families, houses, health, hobbies). A depressing percentage of the people who did work summer jobs are still working those same jobs.

The people who are doing the best had a summer activity, but not a typical teenage job (or even a job). E.g., freelance programming, prestigious math/science camps/competition prep, volunteering and hospitals and in research labs, etc. Years later, you see the dividends paying on an early investment in increasing the value of one's labor.

IMO the blend of protestant work ethic and capitalism on display in the parent comment can be a dangerous one to teach kids. That fantasy is not how the world works. No one gives a damn how hard you work; what they care about is what you get done for them. Otherwise we'd all be digging trenches with spoons.