I also do not understand the RPI detail. (75/90-96/90)= age appropriate.
Most of them are listed at 98/90-100/90
RPI stands for Relative Proficiency Index, and is another way of viewing a student's standing relative to their age or grade peers. It's set up a little like the 20/20 system of visual acuity that optometrists and ophthalmologists use. The 90 after the slash represents the average child performing at 90% accuracy. The number before the slash represents the expected performance of your child on the same task.
Using your son as an example, this means that the test results predict that, on a task similar to the kinds of items on the subtest given, for which most students scored 90%, your son would be expected to score 98 - 100%. The RPI is a lot more informative for students performing near or below average than for those above average, as the spread is not that big in the high range of the population (due to the fact that 90% is the criterion).
