I'm not sure that most of us are talking about shifts in percentiles. My dd, for instance, dropped a number of raw points on science and went up the same # of points on math from the year prior. That is her actually answering fewer questions correctly on one part than the year prior in that one area. For example, and these aren't her actual scores, but it would be like a child getting a 19 on reading one year and then a 15 the next.

In her case, she may have been fuzzy headed since she had a fever I didn't realize until I picked her up, though. She is also an erratic little person, so who knows.

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