DS6 just started using it about 2 weeks ago and I freaked out at first, too! But, as he's gone on and gotten to the real "work" it's slowed considerably. It seems to use how long they take for any particular lesson and average that as if they were going to finish the whole level that quickly.
What we've found is that in the beginning, so much was review (sometimes of things I didn't know he knew, lol) that he whipped through it, easily doing 2-3 lessons in a sitting. Now, he's pretty consistently finishing 1 lesson in a sitting after doing the reviews at the beginning and doing some quick tables. I also just added his timer on to the quick tables to slow down his progress some.
I have a post from a couple of weeks ago with me hyperventilating because he was 46% done 2 days in. After 2 weeks, he's 60% done- still crazy to me, but not "finishing 3rd grade math in less than a week" crazy, lol.
