Grant Lichtman has just suggested a bunch of words better than grit And they all work.
And now it’s time to take on the rigor. Grit and rigor – sounds like a scouring powder or bathroom cleanser rather than a prescription for learning.
Take a look at these definitions and then consider why on earth people would want to associate it with children and learning.
Time to retire rigor, rigors and rigorous from the edspeak lexicon. As Jerome Bruner put it – teaching is the art of intellectual temptation. It should not be grinding in with the heel inculcation and learning is not the breaking of teeth on iron nuts and bolts.
So here are a few alternatives just for starters: challenge, adventure, excitement, elan, temptation, journey, engagement, dare, joy, way of being.
Please feel free to suggest more. 
Well said–it’s high time to retire rigor! It’s another word like grit, in this era of hardening our schoolchildren (as you pointed out in an earlier post). On this same issue, someone once noted that “rigor” in education is best understood as “rigor mortis”–learning that is stiff and dead rather than life-giving and conducive to growth. I liked your alternatives.
Inspiring …..curiosity…..