JR student discount

This website list the following info.
Student Discount
20 percent discount on tickets that cover more than 100 kilometers. Students must be registered as student with JR in order to be eligible. It includes junior high school, high school and university students as well as students of other recognized schools.

Where or how does one register as a student? In Japan, when one buys a ticket or on the internet?

Where or how does one register as a student?

At a railway station by showing your student card of a recognized school. Internet purchase is not possible.

I am not sure whether any schools abroad are recognized. Then again, when visiting as a tourist, the Japan Rail Pass is likely to get you bigger discounts than the student discount.

The discounts are for students IN Japan (you go to an eligible school in Japan).

At my university for example, we had to go to the office administration and we received a special note from the school, along with presenting our student IDs we gave it to the JR staff to get the long distance discount.