Not carpal tunnel, but I find that after grading papers, I have intense pain in my neck, in my right shoulder, and all down the right side of my back (I am right-handed). I must be unconsciously tensing myself up while I'm grading. Today it's so bad I couldn't drive, because I couldn't turn my head or move my arm far enough to shift gears (and I drive a stick shift).
Without knowing exactly which muscles are involved, it's hard to know what's going on, and I don't know how you sit while grading or what your posture is like. But sometimes pain like this can be caused by habitually overstretching the muscles of the upper back, which simultaneously weakens the corresponding muscles in the upper chest and makes them contract. Stretches that reverse this habitual placement by opening the chest and allowing the upper back muscles to contract can help.
The site below has some good stretches, particularly the one for the levator scapulae, though the woman in the picture isn't quite following the directions -- the more you can align your elbow and upper arm towards the vertical, the deeper the stretch you will get:
http://www.hesfit.com/men/comment/shoulder-dysfunction-neck-pain-and-the-scapula/You can get an even deeper stretch if, after you are fully in position, you allow the shoulder of the arm that's down your back to fall away from your ear. (I'm sure that sentence makes no sense to someone who's not doing the stretch!)
This is also a good stretch, though it can be intense, so go carefully:
http://www.healthline.com/blogs/exercise_fitness/2006/10/fixing-upper-back-and-neck-pain.htmlEven the simple stretch of interlacing your fingers behind your back and straightening your arms can help open the chest.
VP