Katie!
We have 13 wooden stairs to get up to our bedrooms/office....
With Nixon, we did what you did for going up, but it still took him well over a week to figure going up all on his own.
For going down, we found that standing right beside him, hand on collar, and kind of leaning into him sideways...almost 'pushing' him up against the wall, helped to steady his body.
He was very cautious and it took him longer to master the going-down on his own.
Ruby, on the other hand, was up that big staircase on her own after 2 minutes in the house...she just sort of bounded up...then stood there at the top, looking down at us.
Of course I raced up and helped her down, using the same 'hold and lean' method as Nixon.
But, she is a clever girl and figured that out on her own in a few hours!