Big or small, it's a 30-year old rule in my whole family that no dog is allowed to go up or down stairs unaccompanied.
Of course, that rule was put in place when one of my grandmothers chihuahua decided that the sewing room/closet (which in our family sees a lot of seasonal use for school clothes and Christmas gifts, but can go ignored for months at a time) was a perfect choice for his personal bathroom. He must have been going in there 3 times a day for weeks before my grandmother went in there to fix something and stepped on 2 piles of petrified poo simultaneously . I'm told the whole county heard the scream of outraged dignity.
I think it's a good rule, no matter what prompted it. I've known several puppies--not even big paw ones--who have been encouraged down stairs with treats, etc., and who have been hurt as a result when they did it alone. My friend Pat's Brittany pup Chippy separated his shoulder when he fell down a set of stairs a couple of years ago. Another friend's terrier actually broke a bone on the concrete floor because of the way he landed. And girl I went to school with almost had a DEAD puppy--their basement was partially finished, and part of it was just an old, old, dirt-packed root cellar--the stairs went right over the slope of this dirt without any backing at all. Their puppy fell between the steps and got wedged in the dirt and very nearly died of hypothermia from being held against that cold, damp dirt for several hours before someone came home from school!
I think teaching stairs alone should be something reserved for service or other special job dogs, just like ladders.Â