It's so rare I have to be in it. I will read and nod off in the sun. I will add PostIt notes and later type these up onto a laptop. I've been known to hide the screen in a cardboard box to reduce glare.
It works for me. I especially like being told when my brain has reached overload and I can sleep for a bit. And potter around the garden to break it up. Putting out and taking down washing. Pricking out seeds. Giving up on the beans and peas. Putting in some more tomatoes.
Sitting a written exam when it is a wonderful day is not so hot; if you have two exams then you miss it all. Not quite a day at work you should tell the student though.