To figure out growth, you have to look at what your school is using as grade level competency levels and not the RIT score, in isolation.
I have some old proficiency charts using NWEA testing. From these it is clear that they test expects more growth per year in the early years than the late ones. So for math the proficiency score is
2nd 185
3rd 196
4th 205
5th 213
6th 219
7th 225
8th 233
9th 240
10th 242
So in 2nd grade, a year's growth is 11pts, but by 9th, it is only 2pts. So when DS was getting scores in the 150's and only made 2 pts growth, we were all happy because it still represented a year of growth at the high end of the test even while his elementary classmates were picking up 10 pts to get their year of growth.
