Amylou, that is my thought - that mastery of the material may become more solid over time. I think that for many high ability kids in particular, it is really easy and quick to merely understand concepts, but it can take time to truly master materials so that they can consistently solve problems, especially non-routine ones, quickly and accurately. Of course, our decision will depend on how " hard" the Math II subject test is for DS. We haven't even look at sample questions yet.