We have to test annually as homeschoolers in NC (it's about the only thing they require of us, so I'm not complaining!)... If we weren't required to I'd probably do it anyway, because a year does seem to make a big difference. More often than that would seem like overkill (not that I'm above overkill... LOL).
Actually DS took the Explore this past January, and the ACT a week ago... so we're officially in overkill.
I don't expect a difference in scores so soon (unless it's an Explore ceiling issue) -- we just did it to compare them, and so the first ACT wouldn't be one that we had to send in to the state!
