"School Students" — what, like there's any other kind of student?

I think this might be a Pennsylvania thing: every so often, you'll see a van or small bus labeled, not "School Bus" or anything sane normal like that, but "School Students".

Whenever I see a van like that, I find myself wondering, school students? Is that as opposed to... ... uh... nursing home students? Courthouse students? Bacon students? I mean, what other kind of student is there?

Can anyone shed some light on this tautology? Is it a tautology? Does it sound normal to anyone who didn't grow up in Pennsylvania?

[Aside: Lord help me, I'm using the meaning tag...]

Yes, this sounds weird. You can come up with a lot of different kinds of students and stretch it to say they aren't technically in schools ("a martial arts studio isn't a school!" Or the abstract route: "I'm a student of life!"). But the underlying truth is that "School Students" isn't a specific enough category to actually give you any sensible amount of information. You don't know what kind of students they are, how old they are, why you need to know they're in the car...

Others have mentioned that it could be because if it only said "Students" you would assume the car was being driven by a student driver. Well... For one thing, I'm still not sure the car isn't being driven by a student driver. What reason do I have to believe that "School Students" can't be a shortened version of "Driving School Students"? There clearly isn't much room left on the sign. Also, even if you do assume that is what it means, I'm still not sure what the makers of the sign want you to do with that information. "There are students of an undetermined type in this car, but they're not student drivers!" What am I going to do differently with this extremely vague piece of information? I don't know if these are preschoolers, college students, kindergarteners... Literally the only thing you know, under this assumption, is that they aren't student drivers. Well, if the car hadn't had a sign at all, I'd probably have assumed that it statistically wasn't being driven by a student driver. So what is this sign telling me that actually helps anything?

Assuming the only logical intent anyone's come up with, which is that the car has young children inside and they are urging you to be careful, I don't think the sign accomplishes that goal. "Elementary School Students" would probably be too hard to read, especially while moving on the road. But you could easily go with other messages, like "Children Inside!" or "Watch Out For Kids!". Or honestly, you could go the most easily-recognizable route and just write "School Bus" on the sign. Yes, it is clearly a car and not a bus. But if a car says "School Bus" on a school-bus-yellow sign, I'm going to assume there are kids in a car and it's being used like a bus. It's not really a huge leap.

So, I agree with you that this is a weird and ineffectual way to get across...well...whatever message it is they think they're getting across. Because clearly we can't agree on what it's supposed to mean. I'm not 100% sure it's a tautology, but in the general sense I do agree it's unneeded. If it simply said "Students", the same (vague and unuseful) message would be conveyed. So it's definitely not necessary in this situation, at least.

what other kind of student is there?

College students. Private students. Home-schooled students. Student drivers.

As Keshlam noted in a comment:

It says "school students" because if it just said 'students" many of us would indeed translate it as "student drivers." Which is a somewhat different kind of hazard. A car full of school students isn't likely to suddenly swerve into your lane. A car full of student drivers isn't likely to have one of them get out and run across the road.