I'd agree with looking for the general trend, and I do for my oldest. A blip here or there is what it is.
Like polarbear said, dd11 has no trend. Especially in reading, we may see scores like: 95th percentile, 55th percentile, 70th, 98th, 50th, 90th... Her NCLB tests do the same. She dropped like a rock on reading and writing from 3rd to 4th. In 3rd, she had a teacher who totally didn't believe in her and she learned little. In 4th, she was in a GT reading class every day with a great teacher who did well by her. The #s seem to have nothing to do with whether she has actually learned anything and, in that case, I was quite sure that her reading and writing capacities weren't worse @ the end of 4th than they had been at the end of 3rd.
I was just unsure if I could reasonable assume that, with MAPS, if she is testing very highly, that she is actually capable of that level of work or knows that much if her scores are bouncing around like crazy. I don't actually think that she's learned a ton in math this year so I don't really see her as having grown 20+ points on that measure. Then again, I think that she knew more than she was showing on the fall math MAPS test.