Yes, this is a difficult exercise for the braille user to get satisfaction from. Even a tactile graphic of the line drawing of Snoopy the cartoon dog holding up a piece of paper with A+ written on it would probably be mostly meaningless.
I agree with Cindi that presenting each quadrant on a separate braille page would allow the student to complete the activity and thus prove their understanding of coordinate points on the plane. [The only alternative to that I can think of is using a poster-board-sized piece of paper for the whole coordinate plane, which would be rather spectacular and really bulky/involved.]
Thank you for sharing the challenge and your thoughts!
–Kyle