We've gone the route of charging for all print jobs since day one; however, we provide a monetary credit onto each student's account into a "Printing Allocation" account which is separated from their campus dollars account (think checking vs. savings). The default print allocation is funded through a portion of the student's technology fees. Departments may choose to provided an additional credit to select students within their program if they desire; however, this additional credit is billed to the department in full at the time they authorize the credit and the funds goes into an account used specifically for the printing service. The printing allocation can only be used at locations that utilize the printing service, and is unavailable for things such as vending machines. The printing allocation is a non-accumulating credit that is reset each semester for active students.
If the student use the entirety of their printing allocation the service rolls over to their campus dollars account if they have funds available on it. If they have insufficient funds between both accounts they are unable to release their print jobs until they place additional funds onto their campus dollars account.
This gives the students the benefit of a "quota" but ties to money and not a page limit/count which makes it easier for them to think about effectively managing their account. We've found that only a small percentage of students use the entirety of their print allocation, with most using less than half, so it seems to be an effective method. This also allows them to manage how they spend their printing allocation (e.g. black & white vs. color, 8.5"x11" vs. 11"x17", duplex vs. simplex, some combination thereof) since we cost the print jobs at the attribute level with a net-zero cost recovery model (the service makes no profit, but doesn't lose money either).
The other method we offer to departments instead of providing their students with an additional credit amount, is to purchase a generic "print card" which they provide the instructor of the course to use during class. This effectively allows the students "free to them" printing during class to turn in assignments. The department is charged the amount placed onto the print card and the funds going into the afore mentioned printing service account.
From the printing services point of view every single print job is paid for. From the students perspective they get a certain amount of print jobs funded by their tech. fees before being required to pay for the jobs directly. From the departments perspective if they want to offer an additional credit to their students they can, but they get charged for it which comes out of their departments budget.
We've had this solution deployed for over a decade. The first year we deployed the environment into our pilot facilities those locations had a drastic reduction (78.4%) in the amount of paper/toner used. Of course this was going from an unmanaged to managed print environment, and not a quota to paid printing so YMMV.