Hello. I haven't yet used RS (will start in the fall with 2 of my kids). My oldest is happily using Saxon (8/7 in the fall) so I plan to keep him with that program.

Anyway, I thought I would give you my thoughts on your question. I typically ask my oldest son to "try to do" the mental math in his head and ask him to explain how he got his answer before our lessons (with no pressure to have it be right)... I do this to assess how much he already knows and diagnose potential problems in logic before covering the material. He is a pretty quick little guy, so many times not only will he come up with the right answer on his own, but he will come up with alternative ways of getting the right answer that I haven't even thought of (that can be very helpful to him in checking his work when he learns the "right" way). I like to do this before teaching him the "right way" because it encourages him to think outside of the box in ways he may not have had I just taught him the concept to start with.

I'm not sure this is at all the reasoning for RS doing this, but I find it useful in my current teaching strategies. I will be interested in hearing the other responses :)