Found a technical manual at http://www.cc.cnyric.org/library/Accelrated_Reader/SRRPTechnicalManual.pdf

So, the score has the same meaning no matter what grade. A table in there gives scaled scores with means and standard deviations by grade from their norm group:

Grade Mean Standard deviation
1 216 95
2 339 115
3 419 128
4 490 152
5 652 176
6 785 222
7 946 228
8 958 285
9 967 301
10 1,079 292
11 1,031 310
12 1,157 299