For state tests, each state has standards that they use to set grade equivlants. They are probably similar from state to state, but certainly not identical. So you can check with your dept. of ed.
For national tests, I'm not quite sure. DS got a GE of >18 on the WJ in "calculation." I am quite sure there was no calculus on that (in fact the WJ just extropolates out for GE's over 12). So in that case it is a matter of how well he does a "lower level" skill, rather than having mastered an advanced skill. Does that make sense?
