Constance Kamii has devoted her career to explaining - and proving - the value of teaching math for understanding. Kohn offers this from The Homework Myth:
Lots of practice can help some students get better at remembering the correct response, but no tot get better at - or even accustomed to - thinking. "In traditional math," says Kamii, "kids are given rules that don't make sense to them, and repetition seems to be necessary to memorize rules kids don't understand." She generally recommends steering clear of homework, "partly because what kids do at school is enough, and repitition is neither necessary nor desirable," partly because when parents try to help their children with math assignments they tend to teach them what they've been told are the "correct" ways to solve problems. Again, this shuts down children's thinking.Part of the problem with automacity is that by definition it invokes a kind of mindlessness - a kind of auto-pilot. But in learning and in life, rarely do situations remain stagnant long enough for us to engage in this mindless, automatic state IF we wish to remain successful.
The next time you are thinking of assigning homework so the students can practice, ask yourself how likely is it that your students will mindfully engage in what you are asking them to do? Or how likely is it that they will do the homework in a way that just goes through the motions?