I believe that if you go to Jim Donaldson's website,
http://www.dallasmusic.org/gearhead/ and read the section titled "What Pro Quality Bb Trumpet Should I Buy" you'll get about as good an idea of the difference as from anywhere else. It isn't realistic to say that "Pro horns have one piece bells".... they all don't. It is equally as unrealistic to say that "Student horns have adjustable 3rd valve finger rings".... Jon Faddis' S42L has an adjustable ring and "he ain't no student".
Nor could one say with absolute certainty that "all student horns have relatively loose valves to allow for dirt, crud, and poor technique by students". That's not an absolute neither... some of the trumepts that are (or were) called "student trumpets" such as the Olds Ambassador are used ON THE GIG by pros today.
It really is an overall combination of the design, responsiveness, sound quality, fit and finish that make a trumpet a "pro model" or a "student model" (although the large marketers would have us believe that if you pay more than $XXXX for a new trumpet you are going to get a "pro" horn) So does price distinguish between "student" and "pro"? Come on.. we know better than that. Does Kanstul 609 or 710 ring a bell? They are sold TO the student market but from the reports could just as easily be used in profession settings where they may even be better than trumpets marketed at twice the price.
So what is it that determines whether a trumpet is a student model or a pro model? My answer would be.... tada.... whatever it's owner decides it is. I currently play a Schilke and will soon be receiving an Eclipse. I am most definitely an amateur (which means..."not pro"). Does this make my trumpets "student" or "intermediate"? I don't think so.
Uhh. there is one label that I think we can all agree on, however.
JUNK from certain Asian countries.