Once you get to the upper level which starts at 4th grade, the explanations drop off. We've used it quite a bit. My DS2 and DS3 use the K format. My DS6 used several different grades. My DD14 used the math section 5-8 for remedial work. The nice thing about using it for a giftie is that it's self explanatory, so they can just go.....

Shari
Mom to DS 10, DS 11, DS 13
Ability doesn't make us, Choices do!