I went looking for the chart that someone posted here a while back, but I can't seem to find it. Off the top of my head, a 255 spring math score is 99th percentile up to about 10th grade, I think.
I don't have the commonly used chart at my finger tips right now either, but 255 definitely isn't the 99th percentile beyond 4th or 5th grade for spring math. I was pretty sure on that b/c I've seen that exact score before for one or both of my dds (one of them in about 6th grade) and they aren't that advanced at math.
The quickest 2011 norms chart that I could find online for MAPS RIT scores is here:
http://www.sheboygan.k12.wi.us/intech/plc/documents/NWEA_2011_RIT_PercentileRank.pdf and it lists 255 for spring math as the following:
99th for 4th grade, 98th for 5th grade, 96th for 6th grade, 92nd for 7th grade, 88th for 8th grade, 85th for 9th grade, 83rd for 10th grade, and 79th for 11th grade. FWIW, that is still a score that would warrant some significant acceleration IMHO.
