One of the issues my wife and I really struggled with in raising our daughter was in the area of discipline. Disciplining a child without an intellectual disability can challenge and exasperate any parent at times. Throw in the "DS factor", and you have a real challenge on your hands.
The question I kept asking myself over and over again, was, "is she getting it?" That is, does she understand what she is being disciplined for? With a "normal" child, you have a reasonably good chance that the kid will pick up on why he/she is being scolded, or punished for an unwanted action. But with a child with a mental delay, I always wondered, and second guessed myself, whether my child was putting two and two together. And so I was never really sure my disciplining efforts were, 1) called for, and 2) effective.
I remember a time when we were visiting my parents, and the subject of discipline came up. I recall my mom making the comment that my dad (AKA Grandpa), in observing how we disciplined our little girl, felt that we were entirely too harsh on her. I would have felt bad about this observation, except for the fact that my mom (AKA Grandma), entirely agreed with us, and felt that our measure of discipline was very much appropriate.
After 17 years, we look back on the whole adventure and think, our discipline was probably just about right. Our daughter has learned what is acceptable behaviour, and what is not. She has learned that she is safe and secure in our love, but also has a keen awareness of what will bring a scolding look or a corrective word when she is out of line. She is well behaved 95% of the time, which is more than I can say for her 2 siblings. We still work on them. But then again, they don't have the years of experience their sister has.