This is from the last page of the norms report:
http://pickens.it.schoolfusion.us/m...ssionid=14d1e9266e4482d198ebc39c6e6bc9c3What is important is that the underlying scale used to measure achievement remains invariant across time. This is a demonstrated characteristic of the RIT scales (Kingsbury, 2003). This means, for example, that a RIT score of 211 carries the same meaning regardless of when the test was taken, the grade level of the student who took it, and what set of norms were in place at the time. This characteristic allows us to measure student growth past a constant scale.
I think you'd have to contact NWEA to get definitive answers to those questions. I'd love to hear their response.
