If you read the MPG-to-MAP (2-5) transition document, you'll notice that NWEA does discuss very high standard errors above certain RIT scores (190 for reading, 200 for math). For example, in the data set shown, kids scoring above about 210 on reading on the MPG were posting absurd SEMs as high as 5.5, which would mean that the typical 95% confidence interval would be a range 22 points wide. This hardly seems like a reliable indicator for teacher evaluations, especially when you consider that the expected growth for a second grader is only about 14 points.
https://www.nwea.org/content/uploads/2015/08/2015-MAP-Normative-Data-NOV15.pdfThe high SEM alone makes this not a good repeated measure.
