I wore khakis, a white button down shirt and a tie to my first interview. I didn’t get the job. But I did get a job later that month at a pizza buffet place.
That’s ridiculous. They’re not going to stack books on the day of the interview are they? No, they’re going to sit at a table and answer questions, apparently from someone who knows less about the job market than they do. Wearing a tailored suit with hand-rolled lapels is probably a sign that he just doesn’t get it, but wearing jeans, or in any other way showing up “dressed for work” is a clear sign that the applicant is not serious about pleasing the boss.
And it’s WARY, dammit.
Times New Roman, 12 point, 1 inch margins. 
Seriously, though, as seen in this thread, some people don’t mind a casual attitude; many do. You can’t do wrong by slightly overdressing or being slightly too formal. You can kill your chances by being less so.
Jeans on a theme park employee??? Unheard of. May as well have a woman with a beard, or a Fiji mermaid.
Of course they are! Interviewing high school kids with no job experience is a crapshoot. I am often literally picking names out of a name. They’re all dedicated to school. They all love reading. They’re all hard workers. The test run for sorting and shelving books is about the only method I have to separate the interviewees.
Book shelver is a minimum wage job. The kid who shows up in a three-piece suit or a fancy dress with high heels is playing the game. I hate the game, so I pay more attention to what they say because those are the kids who try to snow me with what they think I want to hear. I don’t dock people who are well-dressed, but someone who is overdressed for the interview to such a simple job usually doesn’t get it.
You are the exception, however. If you play the odds, overdress for any interviewer. You are far more likely to get the hiring manager for the OP than yourself. You are also the exception in that you have them do a practical and manual labor application.
I just interviewed college interns. I felt a little sorry for these kids in their suits - I seldom wear a suit to the office and they didn’t look comfortable. But they did show that they understood the game. Since what I hired is a college intern in his first really professional job, understanding the game is keeping me from having to do a lot of coaching - and I’m somewhat surprised at how much coaching I’m still having to do.
The interviewer gets to call the shots. If they think that a suit and high heels is inappropriate for an interview to shelve books and that’s what you wore, you guessed wrong. If they think that jeans, even nice jeans, to a theme park interview is inappropriate and that’s what you wore, you guessed wrong. You are probably best off splitting the difference for both interviews - khakis and a button down shirt. But if in either case the interviewer thinks you dressed wrong, you did. Those are the breaks. If everyone guessed wrong, the interviewer might question his criteria, but I’m guessing people showed up dressed in what the interviewer finds appropriate. It may not be “fair” but life isn’t.
Theme parks not only want applicants to play the game, they position themselves as teaching the rules of the game, and they’re often pretty explicit about that. They know that you can spend your summers flipping burgers anywhere, but working at HappyFunLand teaches you valuable skills that you’ll need to succeed in life! Like punctuality, professionalism, and work ethic. In fact, the theme park I worked at lo these many years ago occasionally had workshops and training in these soft skills. (It was this very job that I grew to hate the Pike Place Fish Market so very, very much.) Of course, they’re fairly strict in applying these rules, probably more so than “real” jobs like the ones these kids will apply for when they’re out of college, which is probably why some of it seems to foreign to those of us who have been in the workplace longer; we’re past the need to be taught.
An interview is a test of many things. For instance, is the interviewee prompt? Prepared? And does the interviewee understand what is generally expected of an employee? Hygiene?
Khakis and and a polo shirt, or even a button down shirt, is perfectly fine for shelving books. For the most part, they’re machine washable, and won’t get harmed by shelving. In fact, since khakis tend to be a bit looser fitting than jeans, while still looking neat, I’d argue that khakis are more practical for this activity. Business suit and wingtips or high heels, though, is going to make it hard to shelve those books, and might possibly ruin the business suit. That activity will almost certainly ruin hosiery, too. I speak from experience here…I used to sort and shelve books on a weekly basis as a volunteer at my local branch library. I need to start doing that again.
Now, showing up in party clothes, or in extremely formal clothing, might be worse than showing up in jeans for a minimum skill, minimum wage job. Same thing for offering a CV for that same job…you might as well say “I have no idea what I’d be expected to do as a retail shop clerk, and I assume that you’re vitally interested in my research into Old High German”. It’s appropriate for some jobs, but not if you want to work in a hot dog stand.
Maybe it happens a lot and he’s really tired of it.
But no. I’d never ever advise anyone to wear jeans to an interview. I’ve never even worn pants instead of a skirt and can’t imagine wearing jeans of any color. If the job allows jeans, sure, wear them after you get hired, but not at the interview.