For homeschoolers in North Carolina annual testing can be stressful time. Moms feel like they are being tested just as much as their kids are. No one see the results, but still, it is the knowing that makes all the difference. So, the temptation to prep them so that they score the highest they can is great. But my recommendation is to do no prepping at all for annual tests.
One of the advantages homeschoolers have is that we do not have to "teach to the test." So don't! The beauty of testing in North Carolina is that no one sees the scores except mom and dad (unless mom and dad are braggingly showing them around to their neighbors and in-laws.) Because of this we should think of annual testing as a great tool for helping us be better educators. The results of the test show us where our kids have improved or fallen-behind, what their strengths and weaknesses are, and if we use the same test every year, such as the Woodcock-Johnson, we can see exact improvement in each subject matter.
This feedback is extremely helpful when planning curricula for the next year. If spelling did not improve from last year then a different method of teaching spelling may need to be considered. If you prep your child for the test then the results may reflect how well you prepped, not how your day-to-day schooling went.